There's a solution for this, too: lower the rent to market prices.
> or the cost of repairs to make a place rentable isn't worth the rents it would generate
Well... as a landlord you're supposed to provide for continuous maintenance, and if you have cut corners on this out of greed (like it's common in Germany, just google for "Vonovia Skandal"), it's your fault. And there's always the possibility to tear down and rebuild.
> No one is sitting around waiting for property to appreciate when they could sit around and collect rents waiting for property to appreciate.
You haven't heard of London, I assume? Quote from https://www.theguardian.com/commentisfree/2016/may/04/london... :
> Key to this is tackling buy-to-leave investing, a growing and unwelcome practice. The model is simple, buy a property, leave it empty – in the knowledge that investors do not then need to comply with regulations covering the rented housing market – and sell it on for a profit.