The problem is probably that most people use copyrighted fonts and thus are unable to upload their tweaked fonts – legally that is. I would gladly upload my tweaked favourite font (Underware's Dolly), but I can't. Even uploading the standard Microsoft fonts would be illegal.
However there are a few good free fonts which could be tweaked and uploaded. I'm thinking of some of the URW fonts
(especially Palladio) and Charis SIL
. I may look into it.