I don’t have any resources for you, but I would guess that it is speculators getting into buying houses for resale value, combined with existing landlords who a

I don’t have any resources for you, but I would guess that it is speculators getting into buying houses for resale value, combined with existing landlords who are being forced to maintain low rents due to COVID. When the COVID restrictions are lifted, and the landlords can yank their rates much higher, then many tenants will want to escape those raises, but all landlords will likewise be raising rates. So, there will be no escape if you remain a renter. Therefore, many of those renters are going to want to escape to houses that they can purchase. Which is when they discover that the speculators have bought up all the supply and can now afford to set the sales prices sky high. Oh, and many of those speculators are probably also rental landlords, too.