They are the highest value targets who coordinate the group's activities. Most will have done something at some point that could land them in prison for a long time; this is how they are typically turned. The ones that haven't done anything the feds can feasibly threaten them with often get bribed, which is where things can get really messy because you end up with policing organizations essentially permitting organized crime under a series of conditions (e.g. keep things quiet and we won't bother you). There are many documented instances of this happening on the street level, and some evidence to suggest it is occurring at the national level and the international level. It can be counter-intuitive to think of these organizations being so easily compromised, but a good rule of thumb is that no organization dedicated to criminal or subversive activity is going to evade the attention of the feds, and once that attention is there, they will almost never be able to outspend them. It's comparable to a small business trying to harden their systems against a state actor.