the vast majority of housebreakers are burglars who really hope you don't notice them, they just want to get in and out quietly with your valuables. Pretty much the only circumstance they'll seriously harm you is if they feel threatened and/or cornered.
Imagine the hypothetical situation where you're trying to burgle someone house. You take a gun with you just in case. Now, can you imagine any reason you'd shoot someone in the house other than they are threatening you somehow? Imagine you spot them coming down the stairs with a baseball bat or a gun. Which one is going to make you more likely to just shoot them?
yes, having a gun is a great idea if your facing waves of people who's primary intent is to harm you, but that's just not the case is it...