Maybe i'm in the wrong groups, but I don't see tons of people sharing "fresh" art in Facebook groups, the ones i'm in, it's about the same 3-5 members sharing stuff, and then a few different people selling.
IG has a few people that share art, but pretty much all of them post on CAF as well, but I have found the odd collector that is a comic fan and is a "1 off" comic art purchase. It is a great place to see artists that are doing modern stuff share their work.
CAF needs to update. Their site is a few generations behind the modern internet that needs to be revamped, and they need an app if they want those eyes again (IMO).