The following statements are not directed at any MW:LL clan/unit. I have not joined any units yet, so I'm not bashing anyone in particular. So far the MW:LL community seems to have avoided the problems I've come across in every other game.
There was a time when I was a serious WoW player, in a top-tier guild. I hated those asshats, but it was the only way to enjoy the end-game content. Since I don't need to be in a clan to enjoy the game, I don't feel the need to join a unit.
1) I'm having lots of fun without a clan. So far, I simply don't see why I need to join. Perhaps if the community got larger and an actual league started up I might join up.
2) Time commitment/Time conflicts. I don't have a predictable time schedule, and its going to be rare when I can plan on attending any scheduled matches. Some clan leaders get pretty crazy about making the whole unit show up to these.
3) MW:LL is still in beta. Since the game is very much in flux, with balance issues galore, I don't see the draw in competitive play yet. Perhaps when we hit .8 or so, the game will be mature enough to start taking league play seriously.
4) The off-stage drama. On a long enough timeline, every unit eventually falls apart. Often various strong personalities conflict, create some kind of schism, and splits the clan... or people start leaving in droves so the clan is nothing but and handful of people who can't muster a decent team.
5) The Prima Donnas. The good units attract jerks like flies to honey. I get pretty tired of listening to dbags trash talk, or have their personal tantrums. Then there are issues of Team Stacking and otherwise making me simply not want to associate with certain people. Their behavior ruins my name by association.
6) Voice Chat. #4 and #5 got so much worse with the advent of voice chat. I used the TLL public teamspeak server, and I like it a lot. So its not that all voice chat is bad, its that its pretty much required for team play. Its awesome if everyone is talking about the game we are playing. But most of the time people are just talking about everything EXCEPT the game.