US citizens I believe are having a lot of difficulty getting loans to buy the properties
Also there is much more homes that are needed. Once all homes are bought and rented out the rental market could get much more competitive driving yields down
its already been mentioned this situation makes it hard to keep tenants and there is a large outlay in keeping the property up to scratch - like painting every two years, new carpet etc
not to mention getting ripped by the property managers in the US with tradie kick backs etc