Cops don't enforce drug laws in particular areas because wealthy people live there and not only will arresting wealthy people and their kids get those guys a call from their boss, but the courts will never make any money off prosecuting wealthy people that can afford to drop thousands of dollars on a lawyers and the court case. Drug laws are enforced in poor areas tho because poor people can't afford good lawyers or drag the process out for years and potentially cost the court tens of thousands on just a single case, they instead get give a disinterested public defender, or maybe a bottom tier of private lawyer if they can afford it, against a prosecutor who's entire job is to ram cases and plea deals through the system as fast as possible to make a profit and fund the court and local cops. Judges that don't convict enough get the boots, prosecutors who aren't big enough dicks get the boot, public defenders that don't recommend a ton of plea deals or are too good at their job don't get offered as many public defense cases.

Because many of us who live in cities have experience with police being completely feckless.

I have experienced multiple times when I tell police that I have video evidence of a crime happening as well as evidence of the identity of the criminal and they won’t even look at it. I once had a cop tell me that I shouldn’t bother with a report with witnesses and evidence and a known perpetrator since it would never get investigated. That cop got punished for telling the truth, although they were 100% correct, the detective on the case never even opened the file. The detective was not punished.