[throwaway34241]

If people are just building investment properties to park money that sit empty of course that's not going to help things, it's not really increasing the supply if no one lives there and no one can rent it. They might as well be building a statue or some non-housing object.

That doesn't mean actually increasing the housing supply is a bad idea. Heck, maybe they could have a tax on vacant units to try to force those investment properties that are already built on to the rental market. Or if that's too hard to enforce, raise the property taxes enough where vacant units look undesirable as an investment.

I don't know about the speculative investment market, but at least for the rental market demand is people. I think there are very few people just renting a place with the intention of leaving it unoccupied forever. If there were affordable rental properties everywhere, I think it would be less of a problem even if real estate investments remained expensive.