The gangs exist by selling drugs. Who buys most of the drugs? People from outside the neighborhood who come in to score some coke or pills. Focus on the buyers, and the money dries up.
Of course, then you wind up arresting the kids of judges, politicians, business owners, and all sorts of heat comes down on the police.
In my area in NJ (between Jersey City and Newark) police have a very hard time stopping the drug trade because it isn’t people selling on corners to strangers; it is between groups of friends. Newark has focused on the buyers, but many of the usual suspects you mention weren’t included in the bag because the areas where the drugs were sold were too unsafe for them to go through at night. Newark provides plenty of its own drug consumers; as more young suburbanies turn to prescription drug abuse, they have less reason to ever visit the ghetto anyway.