A lot of working professionals don't want the hassle of also being landlords, particularly remote landlords. If your tenant has a habitability issue, it's your problem. If they don't pay rent and you have to evict them, it's your problem. If they trash the place, it's your problem.

If you pay a property manager 10% to make it their problem, the economics of paying a mortgage on a home you're no longer living in and renting it out become significantly more questionable - particularly in some place like the Bay Area, where mortgage payments are already often more than you would pay to rent the equivalent dwelling.

If you are lucky you can get money from renting. If you were unlucky and had a house in the rust belt and jobs disappeared then few people could buy or rent your house. So people can get trapped. At least you can expunge your mortgage debt with bankruptcy. Not being able to expunge education debt is what's holding our economy down.