In American prisons, there's a unique food chain where gang members occupy the highest tier, especially in Pelican Bay Prison, where this situation is more pronounced as over sixty percent of the inmates are gang members.
Even if one is not a gang member, after entering prison, joining a gang becomes necessary to survive. Thus, many criminals become affiliated with gangs only after being incarcerated, resulting in about eighty percent of Pelican Bay's inmates being gang members.
Still, a small portion of people, despite their difficult existence, are unwilling to join any gangs.
The reason is simple: it's easy to join a gang but hard to leave. Once part of a gang in prison, you're part of it even after release, and it's very easy to be used as cannon fodder.
Every gang in prison makes its presence known, otherwise how could they band together or recruit people? Those inmates who still have a chance of release or hope for parole obviously do not wish to join gangs.