In this specific instance, I suspect it is because there is every indication that the basement room rented by OP was not, in fact, a fully self contained suite within a house, but was a guest room.
How do you physically get into these “basement suites” in your part of the world? When I lived in a townhouse, access to the cellar was via a door in the middle of the property leading off the kitchen. There would be no practical way to split the cellar off from the main property as a separate dwelling. But having guests sleep down there every so often was no big deal.