I'm gonna be honest, part of the problem is Onionfarms is literally just a place I go to, to bitch about KF.
Part of the problem is nothing else is really actively discussed here. I recall back when the news of The Completionist being a charity scammer first broke, I posted about it both here and on KF. On KF it became active, dug up more info, and even got discovered and used as a resource by the people who were investigating Completionist.
On Onionfarms I only got two replies and both were "who is the Completionist? Why do I care?"
And that pretty much says it all: Onionfarms isn't interested in being anything more than a refugee camp where we bitch about KF, and for that reason it will never be as big.
The other problem is that a lot of the people here aren't that different from Kiwis.
I think for a KF alternative to really work, it has to
A) have an identity outside of being a KF alternative.
B) have a culture that is very different from KF.
That said.... the biggest thing that saddens me about KF's decline is that they were an information resource, and when they go, they're gonna take a lot of valuable intel with them.