I see what you are saying about someone in your house, but a thief wants to be in & out and away as quietly as possible! If he gets in & out and then starts your car he has now brought attention to himself, as you and other people hear the sound of your car in the middle of the night, now he can't get it into gear so he's like wtf panics and hopefully gets on his toes, as you are now looking out of the window at him on the phone to the police. It would take a brave thief to come back inside once he's woken a few people up and lights start going on around him.
Or if your keys are taken from the pub, gym, work etc. at least you car is there when you go back to it.
It gives me peace of mind that someone can't start my car, so I intentionally opted out of the keyless start/stop system along with installing a system that protects the car (you need a special beacon to be close to the car to start the ignition).