I'll admit, I've gone off exchanges in the past few years, but it's not really about anyone's behaviour - I just feel increasingly disconnected from fandom as a community. I guess I always have, in that my interests (even when I was small and not online) tended to diverge from what was popular. It wasn't even a conscious thing, my brain just seems wired to pick something that nobody else would/could notice or be invested in and make that my whole personality. So with exchanges, it's hard to find enough common fannish ground to be able to write for someone else. There's also the lag between signing up and actually getting/giving the fic, which I think comes down, again, to my interests being niche; if you're not in a community with a bunch of other people sharing enthusiasm for something, it's more likely to burn out faster.

None of the above applies to vidding, though - I love vidding exchanges. I find it a lot easier to vid for a fandom that isn't The Fandom Of My Heart than I do to write for one.