>Non-occupying owners are a factor in supply and demand; banning them (or even just increasing costs on them, e.g., via taxes on long-term vacant units) reduces the number of prospective non-occupying owners buying and causes existing ones to sell.

The problem with this analysis is that it ignores that homes owned by non-occupying owners (ie. landlord) are still occupied by somebody, and is therefore suppressing demand for buying houses. Or put another way, if you got a landlord to sell a home, there would be one more home on the market, but at the same time whoever was previously renting that home will get kicked out and will also need a home, so the net effect on supply/demand is zero.