These street drug networks are pretty sophisticated and hard to crack down on.
For example a typical street operation like openly selling baggies outside of a legalized injection clinic or to a homeless camp is often done by the addicts themselves, who will always only be holding just enough so they don't see much jail time if they are arrested. Security of this street dealing is overseen by very obvious looking prison gang members who hold no evidence and make sure to never take the money from the street addict peddling their baggies of heroin or crack instead there are drops coordinated with the huge prison goon nearby to prevent any robberies. Resupply is done through complicated handoffs and drops with a network of a few dozen addicts who've been recruited to sell for the gang. The gang themselves are buying off other mid level gangs who in turn are buying from higher level/cartels.
You can try to put a cop on every corner and disrupt the handoffs, or harass these enforcers off the street, but soon your police force is going to run out of overtime money, not to mention the other factor which is gang violence "management". The police know if they decimate the current street gang controlling the street trade that a dozen other gangs will immediately start fighting to be the successor meaning there will be high profile shootings going on in the media, which in turn puts pressure on city hall, which in turn puts pressure on the police chief to do something to stop the violence which eventually means relaxing enforcement on whatever gang currently controls the homeless drug trade so long as they stay in their lane and don't escalate their street violence into the media or against people not involved in the trade. It would be nice to arrest and stop the midlevel and high level suppliers but nobody has figured out how to effectively do that with limited enforcement resources either.