Except it didn't really.
The ball "got rolling" in the sense that Necromancer published some 3e modules with 1st edition design elements and Castles & Crusades, but the real OSR didn't start until OSRIC came out. That was the big splash. While it wasn't an "exact" restatment of AD&D (there were some minor changes to shield it from possible legal repercussions, since nobody had tested the OGL in this way before) it's like, 99% the old game. The target doesn't have to be complete 100% verisimilitude, but it's got to be pretty close. You want people to recognize the old game, keep backwards compatibility with existing 4e stuff and also immediately create a market for more 4e stuff that can work for people who play the old original game or this new game you just made.
And yeah, there is a lot of material but it doesn't have to be all done at once. You don't have to put all the PHBs in one book at one time, for example. Not going to lie and say it isn't alot of work.
Very true.
The fact that somebody hasn't, and the lack of a prominent 4e community in the years since its discontinuation I don't think are unrelated phenomena.