In the U.S. this is often because someone can't work. When you're stuck in a poor area, job opportunities are extremely limited. Public transport is very limited, so you often can't get out of the immediate area to find a job, and most jobs are very restrictive about criminal history.

You can get something minor on your record, and be stuck out of work until you can get enough money to move closer to a place which will hire someone with a crime on their background check, which is now near impossible to do legally.

This situation can make one desperate enough to attempt crimes which can lead to murder, such as armed robbery.

I apologize for being late to reply. @THjr responded very well to this, but there is one more point I would like to lay out. When everyone has talked about these numbers, they've been referring to deaths and that isn't how gun violence numbers work. I understand it sounds like semantics, but when we look at statistics semantics are important. In the modern news cycle, media outlets leave you with the term "shot" and of course we think killed... and in this latest tragedy, it is an unfortunate truth. Any wound suffered is an injustice, but it doesn't mean a death and murder... though, being shot does increase the chance, I understand. Modern weaponry is very efficient (though I'd have to look up the numbers).