The reason these houses are being bought is the exclusionary zoning which makes it impossible to build new ones. The housing market is not free, the government

The reason these houses are being bought is the exclusionary zoning which makes it impossible to build new ones. The housing market is not free, the government has set up extremely onerous regulations to ensure that housing always increases in value, of course investors will see that and want in. The solution here is obvious, stop writing zoning laws that ensure housing always gets more expensive.