Well, rent seeking corporations have driven land prices so high that even a tar paper shack would cost only10% less, so they build at the top end, add 20-30% and you get those mansions.
Corporations are buying with cheap money 1% or so interest. They then rent for 5-6% yield and make $$ like bandits while the US consumer - who has to live somewhere has to pay 50-60% of income for rent.
They need to add a commercial tax rate in addition to the normal building taxes.
That extra tax rate that is only levied on rented houses would shift the balanbe to fewer renters and more owners.