Let me break it down for you. There is only one reason we use handguns, and that is because they are convenient. They’re small, light, and you can conceal them on a person. I would look a little goofy with an AK47 under my shirt.
But in comparison to a long gun, they lack power, and they are much more difficult to learn to shoot well. Anything you can mount on your shoulder is going to be a far easier platform to get fast, accurate hits with.
To put this in perspective, when you shoot somebody in self defense, the goal isn’t necessarily to kill them, it is to stop them. You want the bad guy to stop doing whatever it is they are doing that caused you go pull a gun in the first place. Live or die is really irrelevant. You want them to leave you alone. Sadly, the best way to make somebody leave you alone is to shoot them in their vital organs, and that often results in the bad guy’s death. But that’s his problem, not yours.
So to stop somebody, there are two main ways to do it, psychologically or physiologically. Now when I say psychologically, that means the bad guy quits because he decides to, as in “OH CRAP! He’s got a gun! Run!” Or if you shoot them with a non-fatal wound, and they say “Damn, that hurt. I’m done.”
But you don’t control the brain waves of the critter attacking you. You might get lucky and get a bad guy that will just quit, the kind of guy that if he wanted to work hard for a living, would get a job. Victim with gun = work. On the other hand, you might get some really crazy, evil, whackadoo, who ain’t gonna stop, no matter what. And that guy, you’re going to have to shoot. A lot.