Housing market unfortunately does not conform to the free market rules since its supply is heavily regulated by voting whereas demand keeps soaring in most places. Having secondary instruments like this website only worsens the existing problem.
> In some cases it's justified. But if I just want to invest in a rural house in Arizona that is used as a vacation spot, what's the issue with that?
I think it's because that house is in a community that people need to live in. There are too many instance to count where vacation rentals have priced residents out of their own communities. And when the people can't live there, how are they going to work there?