I've seen many indications that these have increased as a proportion of the housing stock. I appreciate that people have a right to do what they like with their property, but when so many start buying properties that are then removed from the 'primary residence' portion of the stock, we have to look at what this means for society.
You can get large, relatively new houses in Youngstown, OH for less than $150/sq foot. Similar prices can be found in Omaha, NE or Iowa City, IA or Oklahoma City, OK. (For reference I looked for houses with at least four bedrooms in all places.)
This isn’t a matter of the cost of construction. It’s a matter of supply not keeping up with demand due to very very very stringent regulations on land use. None of this has to happen. This is a self-inflicted wound.
The saying used to me that “all real estate is local” meaning that economic trends didn’t dominate local economic trends. Today it’s completely dominated by the Fed.