So says this LAT report - many cops assigned to units that deal with LA's flourishing street gangs would rather switch than sign. The reasons listed in this story is that the LAPD may use personal financial information against them in disciplinary proceedings, and that they don't trust the bureaucracy with the information.
I can see why they wouldn't trust the LAPD bureaucracy. On the other hand, financial info is supposed to be used in disciplinary proceedings - against cops on the take. There's a real possibility here that gang cops have something financial to hide, and intend to continue to do exactly that.