I think in the beginning (before greenlight) they checked all the games.
But then more and more Devs came and they couldn't handle it alone.
Greenlight was a good idea, but in the end a pure mess... With groups that down vote RPG maker games, groups which don't like VN, groups which don't like GG games... It was (still is) a very toxic place... This is what happen, when u (Valve) don't look after your new "born creature (Greenlight)" and let the creature do what it want.
Now Valve decided to lock away the "Greenlight creature" somewhere in a dark corner of their servers...
I think it's good that Valve take over the control again... Sure, there'll be still new bad games on steam.
But no more stupid joke/spam games I hope.
*yes, there're also up vote groups on Greenlight...
Give the power and total control to a internet community.... And you'll have a total mess after 2-3 years ha ha ha...
Btw. the final approval for Greenlight games was never given out of the hands from Valve... (They're not that stupid)
Old school FPS fan, DOOM!!! Why GG not working on my AMIGA 500?