When I eventually stopped playing AD&D and started playing other games, like Deadlands or GURPS, it wasn't because of the rules but was just my brain branching out and exploring new worlds. As I look back upon my GMing experiences as a young adult, and the games I picked up to play when I abandoned GMing, I am struck not by how dissimilar the rules or the conventions of the settings were, but of how different the GMs handled these worlds when trying to craft living, breathing spaces for their players to interact with.
In short, the settings for AD&D were static. They never truly changed and nothing really ever progressed. Even in the supplements and sourcebooks of the 1990s there is this concept that no matter what the players do the countryside remains relatively unchanged, the kingdoms do not fall or expand or shift policy, and there are always evil minions of oppositional gods moving in to the last dungeon that was cleared out or the last territory that was freed from tyranny. You don't have to look very far to see these signs of nothing ever changing.
1) Keep on the Borderlands was a signature adventure module that was released with the basic D&D boxed set of rules in the 1980s. In 1999 a sequel was produced, which showed little changes to the keep after twenty years and largely put the keep in greater disrepair while simultaneously just redistributing enemies among the local cave system to give players familiar with the original module some new surprises.
2) As first described for the Forgotten Realms, Elminster was a powerful wizard who lived in the countryside and could be hired as a sage. There were hints that he was a major player in the regional fighting that went on between the Red Wizards of Thay, Cormyr, Shadowdale, the lords of Waterdeep, etc. He was sometimes described as the magical equivalent of Leonardo da Vinci, yet he never invented anything or actually helped anybody in any meaningful way. Before the first novel had been written about him he had already been imparted outrageously high-level powers and trumps that would easily defeat any player who got it into his head to kill him off. The extant of his powers seems to reach godlike levels despite the fact that he isn't actually a god, and even though his alignment is officially listed as "chaotic good" he doesn't really do many things that could be considered either "chaotic" or "good" - he's actually very "neutral" since he's been in Toril for over 1000 years and yet he hasn't bothered using any of his vast magical powers to build sewing machines or distribute soap, either of which might be considered "good" for a land perpetually stuck in the middle ages.
3) The ultimate status quo of evil in D&D never pushes any boundaries, the bad guys are always repopulating at the same speed and always have the same goals. The ultimate slap in the face to consistency was the Blood War of the Planescape setting, in order to justify that the hordes of evil didn't overrun the planes of existence a protracted civil war between The Abyss and The Nine Hells was devised in order to keep evil fighting one another, because in a very simplified cartoonish world "evil always turns in on itself."
Let's forget these examples, which are only the first three that spring to my mind, and focus on a generic setting. No campaign, no sourcebooks with special rules, just a blank map, a rulebook and a GM trying to create a world. The rules, in all of their iterations, have had classes of enormously powerful magnitude for the level of technology that the world should exist in.
Just think about the potential of a 1st-level cleric. I'm assuming a completely average cleric with no extra special abilities beyond casting spells and turning undead. In almost every edition of the rules a 1st-level cleric can cast 'Cure Light Wounds' a minimum of three times every day. Most commoners are 0-level or 1st-level (depending on the edition) and rarely have more than 8 hit points, which means that a single 1st-level cleric is a walking hospital who is able to potentially save three lives every day. EVERY DAY! Yet in almost every D&D campaign there are always sick, wounded, dying people. From a mechanical standpoint, even low-level clerics are incredibly valuable people to have around. In 3rd edition D&D this gets even more ridiculous with feats that improve spells and give access to more spells.
This is just the average world of D&D.
Your doctor has powers granted to him by his deity, goblins occasionally try to raid your town, and you trade in gold. So imagine walking in to the doctor's office because you have a stomach flu only to be told he's off exploring a cave to the north because he wants to kill some goblins and find some gold. You would be utterly pissed off at his stupidity. You would look at his secretary and say "But I have gold pieces right here, and he only needs to use one-third of his powers for the day!" and his secretary says "But he wants to have more powers, that's why he's off killing goblins." You would think "Why? Hes already making money by being a doctor!" A 1st-level cleric who leaves his village to go off adventuring would be vilified for abandoning his neighbors.
Let's go back to those goblins, let's say your local cleric gets killed and the goblins think "Oh, that town might be ripe for the picking now, they just lost their doctor." and so the six goblins who were living in that cave trundle down to your town, conveniently forgetting that a wizard lives in town. Again, assuming it's a 1st-level wizard who can only cast three spells a day, he potentially has a vast arsenal of weapons to help defend the town with: Charm Person, Burning Hands, Mage Armor, Magic Missile, Mount, Obscuring Mist, Sleep. And again, that's just off the top of my head. Your town has the equivalent of a gunslinging sheriff and he wears a pointy hat with stars.
So, given that D&D has these powerful archtypes, why isn't everybody trying to excel to become a cleric or wizard? Sure, sure, you want to tell me there's game balance and levels and whatever. I'm not talking about that! If D&D were a real world, there's no such thing as levels. In the real world, if somebody could instantly cure three people every day of their illnesses, broken bones, bruises or scrapes, with no long-term repercussions from either the injury or treatment, life expectancy would sky rocket! How many magic colleges exist in the Forgotten Realms? There's one described in every major city and there's even a country that's known for it's red wizard army! In Waterdeep, the rulers are all 30th-level clerics, paladins and wizards, but the ridiculousness of these levels is not limited to the Forgotten Realms. In Greyhawk the setting's central city has nine 20th-level wizards living in it and devoted to the prosperity of the city (and in later supplements there are more than nine of them).
More importantly, in a world where even very weak people can shoot magical energy from their fingertips and put others to sleep with a word and a nod, why is there never any progress? Why are the worlds of D&D perpetually stuck in a pre-Renaissance malaise? This was once the main reason why I stopped playing D&D, the static unchanging worlds feel frozen in time where nothing ever changes or nothing ever really happens.
This is also a real problem for me as a player because I tend to construct characters whose goal is to change things. I don't know how many times I've told the story of my mage-cleric who wanted to build mass transit for Waterdeep only to be hamhandedly stopped by the GM because he personally didn't think the setting should be changed. (This is actually something I have tried to do in every game of Forgotten Realms I've played in since, and the GM involved always prevented me from making progress on it because it would "change the game world" - bollocks to that, I say!) But realistically these thinkers and innovators have to exist in a world where magic is part and parcel of everyday living. This idea that the status quo needs to be maintained and NPCs will not like change is blinkered and stunted.
There's no monopoly on magic. Power struggles and the segment of sovereign rulership that would resist change aside, society might not revolutionize automatically because of magic but change would be an eventuality. Some fictional magical histories last for hundreds or thousands of years and to assume that magic doesn't alter civilization out of the perpetual middle ages is just short-sighted. Our own Earth managed to have a dark ages that lasted for about 400 to 600 years, and that's without the benefit of magic.