The driving forces behind the changes are not entirely congruent with the various editions. There have been several broad "movements" in D&D rules:
1. Making up stuff that people find fun, more or less on demand.
2. Going gonzo for gonzo sake.
3. Avoiding gonzo stuff for some other competing claim.
4. Sub systems for mechanical variety.
5. Consolidating systems for mechanical simplification or balance (simple and balanced not always being in sync, either).
6. Adding details.
7. Removing details in the favor of abstractions.
8. Adding mechanics for "roleplaying".
9. Removing mechanics in favor of the players "roleplaying" it.
And that's just rules, albeit a lot of those rules had goals broad enough to tie into other concerns--such as "realism", "storytelling", etc."
Tracing those movements in editions is like trying to trace religious movements in, say, the last 500 years of Western Civilization. You can make some broad statements that will be generally true as long as you remember that the movement does not even come close to explaining all the changes. It contributes, it does not account.
#5, consolidation started strong in 2E, gained traction as 2E went along, stayed strong throughout most of the 3E cycle, and was still kicking pretty heavy through 4E so far. However, the exact rules target of that consolidation has varied considerably over that span--not to mention the counter-reaction to it. And the spirit of it was very much present in some 1E discussion, and even showed up a bit in the RC rules.
One of the bigger changes preceded the OP's benchmark: When Basic decided to have different die sizes for weapons. Before that, I believe it was 1d6 for each weapon. You flavored to suit yourself. (There might have been an interim period where fighters got 1d8 and wizards got 1d4. I'm not sure.) This marks, I believe, the start of movement #6 (details) as a movement with real teeth. People have been pushing it and reacting against it ever since.
