I think the more important question here is, who is going around fitting doors on all these caves? Also, Wolves are able to open doors/pass through load doors, I've seen it happen many times.
O.o
Anyway, I'd think that most bandits would be independant groups formed either before becoming bandits or during the course of upcoming banditry. As to larger groups of bandits, I'd think that either: A)the legion could get rid of something large enough to be considered organized, like the mafia, while not being like the Dark Brotherhood or B)you don't talk to the bandits, how do you know they aren't all working together (or at least some of them)?
Seeing as how bandits rarely write books, settle down for an interview, or likewise inform us of their intentions. Until you can join a bandit group in TES, they really can't be proven or disproven :shrug:
As to the strange caves, no one said they were logical, nor are wolves, but it is far more convenient for AI and the building of caves that you can't just fall into one. If you really want a more realistic experience, try a mod^^.