Why is Inventory Low?

[Manco Snead]

Ok, inventory is low right now. What has made it low relative to 5 or 10 years ago when it may not have been low? Yes, a lack of building, but a low inventory is only low relative to the number people looking to buy. So, has the US population simply increased? Disproportionate number of short term rentals? Wealthy people with second homes sitting vacant?