Perhaps greed is a factor in non-enforcement, but I suspect in LA it's more of a "overly humanitarian" subculture. See Echo Park protests. bodies were turning up in that park, and it was unusable for local residents due to a massive encampment and rampant drug use. When the police showed up to clear it, they met actual protestors from
outside the neighborhood who thought it was inhumane to force the campers to move on.
I lived in Studio City for a bit. We had a well-known vagrant who lived under a local bridge who regularly accosted women, including assault, groping, etc. The nice walking paths along the LA river, and the immediate neighborhood around them were completely unsafe even during daylight hours for my wife and daughters to walk along. What could be done?
I lived in mount washington for a bit. There, the citizens would quietly organize, bring lots of shovels, and go "clean up" even the smallest encampments. I suspect if that word got out, they'd meet protestors, or even police.
I'm all for helping those who need and want it.
The trouble is, there's a significant enough population that doesn't want help, and wants to camp and live among drug use wherever they choose. This is the only case where "Not in my backyard" makes absolute sense. Police can and should protect the safety of neighborhoods and parks which are funded and occupied by tax payers.
Go to venice. It looks like a third world country. Last time I went to the beach, none of the shops were open and obviously-mentally-ill people were sitting in their own filth on residential and commercial doorsteps. One obviously intoxicated person was holding a can of gasoline on the sidewalk, and swaying between cars he didn't own. What good can come of this? The rights of the people in that area need to be balanced against each other through the use of local laws and law enforcement. We've gone way too far past "balanced" towards an ideologically-forced tolerance of vagrancy.
It is not the job of the average citizen to come up with solutions, it is normal and fine for citizens to collectively demand change from their government and to weigh the outcomes during the next election cycle. My own lack of ingenious ideas for it does not mean I need to be silent and tolerate the solution.