Nostalgia.
I hear a lot of people talking about the rules and how the rules are simpler or lighter or more empowering to the DM, and things like that. And as a long time 1e DM, I just don't buy that.
What I do believe is that over time people began to subtly change the way that they thought about games, and that this change in thinking went with changes in rule systems. And I think eventually, people looked at how far they'd changed from the games that they played in their youth, and they said, "You know, I want to play like that again. The game I'm playing now isn't a game I'm enjoying any more." And for most people, this act of changing the idea of how to play a game had to go hand in hand with changing the scenery back to that which surrounded the game when they were younger, because otherwise they would have fallen into their new habits. In other words, they had to go back to the old rules to get back to their old way of thinking. And when they did so, it was probably a relief, and it was definitely a change, and they enjoyed themselves as they hadn't enjoyed themselves in a long time.
I just don't buy their explanation for why simply because I'm too familiar with the old school rules and what could and did go wrong. No phrase over the last five or six years has baffled me more than "Rulings not rules". What game were you running that didn't require rulings, and maybe more to the point what game where you running where your rulings were not relied on as much of a part of the social contract as your rules?
I tried to go back to 1e AD&D a few years ago, at least as an experiment, and I couldn't do it. For one thing, it was too much mental overhead during play. Things that would have been incredibly simple to adjudicate in a unified system became absolute nightmares in a system with unlimited crunch except for what you needed right now. With no one mechanic to turn to, I was left paralyzed by too many choices. Should I use the incredibly detailed but ultimately vague system proposed in the module? Should I just use a straight up percentage check pulled out of the air? Perhaps I should ask for a saving throw? Maybe I should use a roll under ability check? What would be fair? What would be expedient? Would I be happy with this as a precedent? Sure, those sort of problems turn up in modern systems as well, but they don't turn up as often and in particular they don't demand as much 'run time' because I can solve them at 'compile time'. Sure some DMs don't care about consistency or neutrality of fairness, and I guess that's ok too if everyone enjoys the ride, but I'm not that DM.
For me I play 3e exactly the same way that I play 1e[/e] only it's less fiddly and I don't have to make up as much crap or interpret as much vague text. Granted, to accomplish that I banned everything but the core rules of 3.0e, never adopted 3.5, and then ended up rewriting half of that to get it where I wanted it... but all of that is normal for how I run a game. (To prove that, see the thread in the 1e forums where I experimented with completely rewriting 1e dragons, as a first stage toward completely rewriting 3e dragons).
If anything, 1e vastly disempowers the creativity of the players compared to 3e.
The idea that you can't remove PrCs? Did that 16 years ago and never looked back.
I had a 64 1/2 Ford Mustang when I was in High School. I loved that car. That car was manly and cool and I had a lot of fun with that car. But I would never want that car as my primary vehicle again. Sure, I could get under the hood and fix almost everything on that car, but I had to get under the hood and fix everything on that car all the time, or it would leave me on the side of the road stranded. Going back to 1e AD&D felt a lot like that. But I totally understand why some people want to go to OSR.