> They just rent it out.

This is not the case in some prominent housing markets (London & NYC come to mind). There are owners who purchase the properties as a way to store wealth in the US. These dwellings frequently sit empty most of the time.

The Dutch had a great system where buildings that had been empty for over a year could be squatted.

https://en.wikipedia.org/wiki/Squatting_in_the_Netherlands

I learned about it after a trip to OT301 with some friends from the CouchSurfing meetup in Amsterdam in 2013. Apparently the law has changed though, and now people are being criminally charged for squatting empty buildings.

In California, you can gain possession through adverse possession with about 5 years if lucky. That is, squatters rights exist in theory.

Why yes let's just violate property rights to fix a social problem

There will always be a balance of how good a house is an investment and how accessible owning a home is.

Investing in housing can decrease housing availability especially if investors are using it for short term rentals.