11 pages and no answer?
Lots of reasons why someone might prefer pre 3E, but none on the timing.
There where always people who played 1E or B/X and some that stuck with 2E. But thats OS, not OSR.
The Pandora's box was cracked with 3.5, and hurled open with 4E. Check the dates on a lot of OSR blogs, or even the term OSR itself. OSIRIC came before, but the surge starts in 2008, and its not a coincidence.
People rallied around 3E. They liked it, and wanted to believe in it. And 3.0 has a lot of AD&D in it.
Eventually people began to say things like "NPCs are too complicated" and "Perception is a problem", "what is all this crap in [player oriented book X]" and "check out Dragonsfoot"
But there weren't very many of them. OSIRIC and Labyrinth Lord helped open the door further. But 4E, and WotCs attack on 3E, broke the consensus and made people wonder what other D&D they should try. OSR and PF are the beneficiaries.