I make the bed as soon as I get out of it.
I don't know why? It is just something I always do in a morning, usually the minute my feet have touched the floor.
I go into my kids rooms, and since we have lived here, I resist the temptation to straighten their bed.
I have my own reason for making mine when I get out of it, I dare say they have their own reasons for leaving them unmade. Although it could just be plain laziness.
I suppose it goes back to when I was young and Mum was working, so she didn't always have time to make our beds in the morning. Saying that, my sister always tended to leave her bed unmade, and still does now, and she's been married 29 years!
Ah, well, each to their own, but I like to get into a made bed at night, and not have to start straightening out a sleep tousled one.