The greater good
So if you happen to be a gang and get caught by the police doing something illegal, that does not mean your comrades will fall with you. Because biker gangs can technically classify themselves as clubs, it is very hard to pin the whole club for the crime of one member.
They usually just say that the one member who got caught by the police was acting as an individual and does not represent the group. In this way, they are able to protect themselves from ending up in jail if the police raid them at any point in time. This also explains why they are so difficult to arrest in the first place.