Who knows dude, could be myriad reasons. No enthusiasm from Geffen to do it, lack of archival recordings pre-1988. Don't know the sales figures from the previous reissues, but maybe Geffen figured they nailed the three most well-known/popular albums and they got other fish to fry. Sucks for us hardcore fans.
I want to see more archival live releases a la Live at Smart Bar personally. The fact the band isn't active anymore also probably contributes to a lack of enthusiasm and energy for more releases.