Im a woman, but here what I know about making beds.
1# learning it as a child to teach them discipline (though I think this as taken from a book in Germany about the SS youth)
2# Representation to guests. A neatly made bed is nothing to be ashamed of. (Especially if you're a host or own a hotel or something with sleeping arrangements)
3# Making a bed (in my own language), I was told that it was derived from 'making open' (more or less literally translated) and that it was to help the sweat and such evaporate from the blankets and matrass, keeping them not only smelling fresh and clean, but to inhibit bacteria and the like from growing in damp areas.
Health reasons.
Also, futons are also needed to hang out and to be taken proper care of so that they'll last.
It's quite likely but not many people do it nowadays, and also, not every item that you sleep in needs this kind of care with modern materials.
And the 'making open' they don't mean to place the blanket over firm over the entire bed, but to fold it up on the end where the feet lay when you are sleeping.
Also, if its of any relevance to you, I don't usually make my bed either. Never been a habit of mine.