Obviously I cannot speak to what the situation is in the US, or even necessarily the entirety of the UK. I can just say that in my specific geographic area, it is largely second homes, holiday homes, AirBNBs, etc that are the problem, because the number of houses lost to the residential market through this is pretty much exactly the same as the number of households currently legally classed as homeless (which often means not necessarily on the streets, but being “housed” in hotel rooms and the like). If every single house that is not currently being used to home a family was confiscated from the owners of second homes, holiday lets, AirBNBs, etc and repurposed into residential housing, there would not be a housing crisis here.

Private landlords have, obviously, been raising rents in the last few years, but a big part of that is a matter of supply and demand. If one house gets 50+ families applying to rent it, of course prices are going to rise. We don’t tend to have multi-millionaires buying up huge swathes of houses here, with the average property “portfolio” being less than 5 houses. It’s simply not possible to get thousands of individual landlords to collude on prices, so if the actual problem - a lack of houses available to live in - was fixed, competition would be sufficient to keep prices under control. If no one is applying to rent a house because they’ve already found somewhere else to live, prices will drop quickly.