Why do people sleep together?

I've always wondered why so many couples like to sleep together, even if they could afford separate rooms and separate beds.

When you sleep together, you have only half the usual bed space. The bed gets too hot, the other party snores, farts, steals your blanket, steals your pillow, rolls right into the middle of the bed, pushing you out, and accuses you of doing all of the above in the morning. Or else you can't fall asleep properly for fear of doing all of the above to the other person. Or you wake up during the night and want to read in bed and have some tea, but can't do it because of the other person.

It's fun to have sex or simply hang out with a guy in bed, but usually when one of us starts to fall asleep, I want to be out of there and in another bed.

Don't get me wrong, I am not surprised that some people enjoy sleeping with each other. But why so many?