In the GTA series, the various cities that the games are set in are usually rampant with crime. If it isn’t the player characters going on a rampage, then it is either the police, or the other citizens that will be easily driven into a homicidal rage for such minor things as being bumped into while walking down the road/minor collisions.
Why would anyone bother to live there? It seems wildly unsafe, even before the various other criminal enterprises get involved.
Same as in the real world. Poverty prevents mobility.
You can’t really just move, unless you enjoy being homeless and jobless. You have to prepare to move by finding housing and either income or cash reserves. If you’re already impoverished, you have neither the time or resources to do that, unless you’re moving somewhere that you have people to support you short term.