idk.. like I said, i feel the SD userbase (as far as mod devs go), is like a pyramid:
plugins at the biggest, lowest tier; part mods smaller in the middle; planet packs at the top in lowest numbers...
i just feel a lot of part mod devs are/have been disenfranchised from from hosting on SD cause of this issue everytime they wnat to upload... 
probably doesnt help that upload bandwidth goes thru the roof right after a KSP update... which is when devs want to push their updates