– neither your head nor your pillow go off the bed, because the wall is there, so you don’t even need a headboard.

– if your head is towards the wall, then you get a view of the whole room instead of the view of the wall and you don’t turn your back on the room.

– you might put one of the side of the bed against a wall but then you lose one exit side from your bed (annoying if two persons share a bed).

You will notice that in a lot of ads that sells beds, the bed (with headboard) is rarely placed against the wall, very often it’s placed in a crooked way like somebody moved it to vacuum under…

To sleep in the reversed position would be less handy because everything is out of reach. The solution would be to move the tables and nightstands also at the foot of the bed. Now would you really want to trip over your nightstand every time you went to the potty in the middle of the night?

Psychologically speaking, maybe subconscious from generations ago, the head is kept farthest from the door as a form of protection from an “invading force”, for example, burglars?

you can also keep an eye on the whole room for burgerlars/intruders

you wouldnt want to wake up facing a blank wall

like sofas headboards look weird in the middle of a room

It’s so you can get out of the bed quickly when needed… all kinds of reasons!

It’s probably a survival tactic from when we lived in caves. Never turn your back in the enemy sort of thing.