Burglars aren't (necessarily) idiots, and it's one thing to go to jail for burglary, quite another to go to jail for murder or aggravated assault during a burglary. Their priority is getting money or valuables and then getting the hell out; if the homeowner catches them in the act, that's a very bad thing regardless of whether he has a gun or not. There's very little point in bringing a gun if you don't expect the homeowner to have one of his own.

Of course, if it's a tiger kidnapping or carjacking, it's a different story, then the attacker is actually looking for the confrontation. Burglary, not so much.