Not a lawyer but probably to safeguard the tenant rights.
Imagine you are a tenant paying monthly dues and suddenly one morning you are told by your tenant to look for a new house. You have no clue where you can find it. You have already used up your salary in the last week, you have a family along with you. So I think it protects tenants from this type of situation.
Or else tenants could easily give you a room and then when someone pays them more they would have given that room to them.