If everyone had $40k/year of guaranteed income, all of a sudden opportunities to go around slumlords opens up: they can buy land and new-build or redevelop housing with UBI-Backed mortgages (so the bank knows they’re getting the money back).

Renters almost by definition aren’t capable of amassing enough capital to build new housing, so are at the mercy of the existing supply. If it is guaranteed that everyone has a capital-amassing stream of income available to them, they gain an ability to turn that stream into something longer term. Sure, this still may not be possible in areas with strict housing regulations, but a guaranteed, portable stream of income also provides people the means to move.