Depends. Most wolf packs die fast, but from what I know and noticed, the reasons seems to be the same. The game is pretty much overrun of canine oriented groups, whenever you enter a map, there is bound to be at least 1 pack roleplaying, or nothing. So this means there would be a lot of competition, right?
Unfortunately not. One of the main reasons I leave wolf packs (and stopped roleplaying in packs too) is that normally they rather only roleplay between themselves.
So this means most groups only focus in, well, 1 group, and rather not meddle with other groups (having allies/rivals),
and that's a major downside.
One of the most exciting things about wolf packs, for me, is their relationship with other animals/wolves. But most groups nowadays? Prefer not to have to talk with anyone but their own members. Since there is no confrotation, they mostly roleplay their lazily laying around or pretending to catch a NPC prey. All I have to say about this, is... BORING! If there are no danger, or anything to waste all of the adrenaline rush, them it's only a "Lay around simulator" for me. And you know how many FH RPs are "lay around simulators"? A lot. Really. When I want to join a animal roleplay I'm not looking to sit near the den and socialize with other members. Normally I'm looking to act as an animal, feel hunger, thirst, having to confront and compete for territory and food. And in the middle of all that action, socialize. This is one of the few things I like in warrior cats groups, since they are clan-oriented, there will always be confrotation between clans. It's a shame I'm not a fan of housecats, really.
Another issue is originality. Since there are a lot of wolf packs, repeating ideas was bound to happen. Which means you can easily hop in groups with not much change. So if you want your members to stick to your group, you will have to offer something unique.