That's just like the fishing net used as a hammock instead of catching fish. A house used for housing is a productive purpose. It is generating value to the economy every minute that it is being used as shelter for humans. That value diffuses out to more people through trade. When used for speculation, it is not producing value, but simply storing it for later use. Meanwhile, those who would otherwise produce value from it are producing less value in aggregate because they are denied access to at least one house.
If you put gold in a vault, it retains its value. But it cannot be used productively. If you instead loan the same gold out, you can charge interest, and some of the value generated by the gold performing its productive function as money will diffuse back to you via trade.
As a whole, the entire economy would prefer that all tools be put to productive use 24 hours a day. But the individual Nash equilibrium strategy is to selectively employ or withhold the use of those tools for greater personal benefit to the tool owner.
In the government's role as cartel enforcer, it would be in the interest of the whole cartel for the enforcer to levy a vacancy tax on investment properties. That reduces the personal benefit of idling the productive tool, but the enforcer then also has the burden of returning that value to the economy in a productive way.
If you put gold in a vault, it retains its value. But it cannot be used productively. If you instead loan the same gold out, you can charge interest, and some of the value generated by the gold performing its productive function as money will diffuse back to you via trade.
As a whole, the entire economy would prefer that all tools be put to productive use 24 hours a day. But the individual Nash equilibrium strategy is to selectively employ or withhold the use of those tools for greater personal benefit to the tool owner.
In the government's role as cartel enforcer, it would be in the interest of the whole cartel for the enforcer to levy a vacancy tax on investment properties. That reduces the personal benefit of idling the productive tool, but the enforcer then also has the burden of returning that value to the economy in a productive way.