It's economics. Killing Floor is a $20-at-most game that they've already completed and is in a "Stable" state.
RO2 is a $50 game that just released and needs immediate attention to fix a ton of bugs and lag issues.
So they're gonna drop KF like the red-headed-stepchild while they fix their bigger moneymaker. Sure, they'll probably have some "Events" where they have reskinned enemies and a few achievements you can complete to unlock skins...
But, at least for a LONG time, the good old days with our free content updates and constant dev attention are over. I'm glad I played it in it's hayday, because it makes me kinda sad to see KF in the stagnant state it is right now.