I've seen a lot of posts on the nature of the shift from O/BX/AD&D to 2nd and beyond both in the nature of the rules and their proliferation. Many of these posts have been very helpful for formulating how I want to play D&D, and enlightening besides, because I'm interested in this stuff. (Learning about the history and evolution of your hobby is fun in itself.)
The general consensus seems to be, broadly speaking, that the earlier versions of D&D were naturalistic (according to a pseudo-technical definition evolved in the OSR), 'objective' (by which I mean the world didn't change to accomodate plot or narrative, but rather treated those as emergent qualities), and action-focused, rather than character-focused.
One of the myths of the OSR is that rules proliferation was driven by an attempt to make the game "fair" and curtail the power of the GM as used for evil. By myth I don't mean to imply its falsity; I mean something like a cultural story. Personally I think there's good hard evidence in the way certain rules and mores in our hobby evolved for this myth. Further, even beyond questions or truth or falsehood of the essential facts, the myth is good and useful, because it makes us think about social interaction at the table and form the correct response to the spectre of social friction.
However, I don't think it tells the whole story. To that end, let me offer another explanation, meant to go side-by-side, rather than replace the above.
Most OSR bloggers I have read got into the hobby as kids in the 80s. These folks cut their teeth on B/X or AD&D with their brothers and neighbors, with lots of time and the general social difficulties children have influencing their gaming. It's true, there are bloggers out there who started in the 70s, or as adults, or in the 70s as adults, but I feel pretty comfortable saying that the lion's share of the OSR bloggers out there to whom I have been exposed either are the children of the 80s or strongly influenced by them.
I have a different perspective. I started gaming in the 90s, with GURPS - with adults. (I was three.) By the time I started regularly playing with people in my own age group, I was in college. So I largely side-stepped the difficulties of gaming with (other) children, who haven't fully developed a social consciousness. I never really experienced the difficulties of an unacceptable adversarial GM relationship, or gaming with people who can't be 'adult' about things.
One of my other hobbies is mucking about with computers. This is hardly surprising; there's a large intersection of gamers and computer hobbyists of all stripes. One thing about computer hobbyists, no matter what distinct strain they adhere to, is that they like tinkering with things and building things. For some it's more mathematical constructs, others play with soldering irons, still others like creating and refining software.
I think those urges spilled over into the hobby of gaming as well. People started making new rules not just to fix what they considered broken but because they wanted to improve the system they used. Tinkering with improvements and redesigns, while putatively useful, is actually often an end in itself. Some people garner enjoyment from the tinkering.
This same thing happened with rules. I posit that some of the rules-creep that happened happened because people enjoyed making rules and having rules.
Unfortunately, while the process of making rules can be fun, and being able to say you have rules is enjoyable, the actual use of those rules can be a real bear. Especially when those rules were made at root for the fun of their own making, with actual play being secondary. (c.f. AD&D's weapon speed factors)
This urge is still with us today, and while we have a cautionary tale against changing the game to make it more 'fair' I haven't yet seen anything like a consensus narrative addressing this problem. (Peter's Has that come up in actual play? is the pioneering exception, for which the man should get massive kudos. Everyone coming here already knows about that post, but go read it again.)