You are confusing cause and effect.
The people who care moved out of the bad neighborhoods long ago...no point in buying a house or staying in one in a high crime area if you can figure out any way to bail.
There are some sweet old ladies that do live in the bad neighborhoods because they are poor and cannot figure out an alternative—if they get out of line they will be dead old ladies as their houses get burned with them in it. They do care—about staying alive.
No, I’m not. We know from all the stats that it’s the caring that goes first. Step 1 of a neighborhood going down hill is not replacing the street lights when the burn out. Criminals are lazy, they don’t put in the work to ruin a neighborhood. They find a neighborhood that’s already lost.
The problem is the people who let it get that way so the sweet old lady was trapped. Every Projects we had in this country started nice. But they didn’t care, and it became bad. We’ve got this crap documented in neighborhood after neighborhood after neighborhood. And it does NOT run the cycle you say. That’s the plot of bad movies. Reality is much more tragic. The people in the neighborhood stop taking care of it. It becomes dark. And run down. And the criminals moved in. That IS the cycle. Has been for decades, over a hundred years, in America, Europe, Asia. You want your neighborhood to be good, start by keeping your house up, then help out your neighbor.
And stop watching dumb movies that make it seem like gangs just pick on neighborhoods. Really if gangs were going to take a neighborhood down Bel-Air would be a ruins. Think about it, bunch of rich unarmed liberals with lots of cool stuff to steal. That’s a place worth targeting. But the people there keep it well lit, and well repaired. No gangs.