The theory I've been running under is that Rivers went a touch mad from becoming popular, and in his spiteful rage he decided to release nothing but crap after Pinkerton. Well maybe he wasn't entirely focused on the crap plan for the green album, but he was fully committed to after it.
Now, even though he wanted to spite the music industry and prove that they can sell crap music, he still wanted to make good music, and Weezer still could make good music. So the second half of his plan, or the "not-full-of-crap" part of the plan was to write all this excellent music, record it, but never release it, save for some small, rare little demos. He then took his fortune from the rest of the music, and used that to secretly fund weezer fan sites and servers that would run popular peer to peer software sharing the music that was worth hearing, the music Weezer wanted to make, so that the fans would always be able to download and share the true meaning of love Weezer.
At least that's what I keep telling myself. That's the only way I can rationalise it anymore...