Many of the FR titles were crunch light.
Quite simply, the ones that sold less are less remembered.
But the pattern was also present for 3PPs.
Was there ANY 3.x book produced by WOTC that didn't have at least one option for players, i.e. a feat, spell, race, class (prestige or otherwise). Only the monster manuals come to mind and even those had things like the LA races....
Indeed, I remember many a complaint that WOTC was "taking advantage" of players by having player-crunch spread throughout ALL their books.
EDIT: Getting back tp the OP, I think ggroy is right....
If the compendium, monster builder and character builder were up during the start of the 3.x era, there would be no 3PP either even WITH the more open OGL. Throw in that WOTC actually updates the compendium with their errata....and I think 3PP would be looking at a serious challenge...
During 3.x, there really was no difference between a 3.x sourcebook produced by WOTC and a 3PP in terms of how easily it was to integrate the material into an existing campaign...
It took just as much effort to rewrite an encounter with a new CR X monster if said monster was created by WOTC OR a 3PP. Now though?
Not even 5 minutes with the compendium and monster builder....looking at easily 20+ minutes with a handwritten encounter...