> Why don't landlords undercut one another? They literally don't have to. The only outcome is less profit. You'll find a tenant eventually, at any price.
is very obviously not true, otherwise prices right now would be effectively infinite. Why are prices for an apartment in SF only 3k/mo instead of 30k? Surely under your reasoning a landlord could just wait and get a tenant at any price they set?
The answer is always supply and demand. As long as the supply is constrained or demand goes up faster the price will rise. But UBI doesn't change that math at all. (I say this as someone not actually a fan of UBI)