Most armed criminals who are really around for awhile, not broke drug addicts who indescrimently rob you on the street or hold up liquor stores, are out there making what is considered great $$ by working folks.
A drug dealing gang banger is probably not going to stick out their neck to steal anything except a load of cash from another rival gang - they are going to try to stay under the radar and use their financial means to secure whatever they need (which could come from theiving drug addicts or a more organized source).. if you have the $$ you can pretty much buy anything.
There is a lot of cold steel out there, for instance when someone dies a huge collection can instantly disperse without any legal ramifications even in a state with strict controls/tracking. Often on the grey market a regulated thing like a gun is worth more, so there's motivation to sell them under the table.
My point is, the criminals doing most of the killing are probably not stealing their guns.
I agree, especially since most experienced drug dealers know that they can count on customers with clean records to buy guns legally and exchange them for drugs. That's a problem here in Maine where we respect gun rights but are dealing with people who have direct access to major drug supplies and also live in states that restrict gun rights like MA, CT, and NY. It creates an unfortunate free market exchange.
The problem isn't simply the hard case dealers. It's also the high local population of drug addicts who fuel the whole thing. From the perspective of someone who grew up in a major city and moved here it feels like a significant population of addicts includes a segment of locals who are figuring out how to be real gangsters.