I've only seen one catgirl avatar on this forum, but to be fair, I'm not here like I used to. I still don't see how it correlates to having a fetish.
Catty behavior is probably generally well-liked by certain men because the girl gives and wants affection. You can stick any tail or ears on a hot/cute girl if that's you're thing, and it wouldn't matter if it's a cat or not. At that point, it's just a hot girl in a suit. They just seem to be the popular trend, probably due to implications in personality and behavior rather than furry fetish fantasies.