My opinion is that most US street gangs are extremely disorganized(i.e. the crips and other gangs started out as one unified group and broke down into squabbling, individual sets and groups) Because of the lack of leadership and organization, the government doesn't consider them an extremely serious threat. If they were unified and organized the US government would consider them a larger threat. The organization, rules and structure is a large part of what made the Italian-American mafia so dangerous (and in the last couple decades the government has managed to break down the organization/structure of the mafia - making them less dangerous as a group).