Because if there's a small town and you book the only room in a B&B there... but don't turn up or book it for a whole week or whatever. If you deprive someone who is actually in a position to use this room while you are not, you are being a dick and breaking the rules.
It’s an advantage. Say I live in Germany or speak many languages, I can book more rooms or find better places. Or if I have endless time as a lazy student I can research and book places.
See it or not, it’s an advantage that some might not be able to do. So it just levels the field.
Because if there's a small town and you book the only room in a B&B there... but don't turn up or book it for a whole week or whatever. If you deprive someone who is actually in a position to use this room while you are not, you are being a dick and breaking the rules.