Actually, that is a big part of the rent problem in Spain. Getting rid of squatters is hard enough, but getting rid of a tenant that stops paying takes even more time and effort. And you are still legally bind to pay for utilities, even though you are not getting any money. So people prefer to have an empty house than to rent it to a person they are not sure will be a reliable payer.

And if they decide to rent, that includes demanding the tenant has a stable job, running debt checks on them and asking for several months rent in advance, which makes more difficult to rent for people with low wages.