Depopulation and inability to pay for higher prices.

Immigration is one of the leading purposes of decreasing housing supply, so that will help to some degree. However, there's another problem of just a decreasing population which can't really be contained. Gen X had less kids than GG'ers did, and Millennials had less kids than everyone before them. Gen Z and Gen Alpha are barren. The demand is technically high for housing, but as Boomers die, no one can replace them. Either institutions will have to expand massively their ownership of property, or they will simply enter onto the market, and be too expensive for their family or bank to profit off of. Hence, prices will have to come down because these younger generations simply don't have the savings to afford these houses.

"Okay, but couldn't they just rent the property?"

Not if they need the cash right now. Renting comes with managing the property, and that's expensive. If it's not worth it to keep, they'll sell it. And there's such a glut of rentals at this point that there's barely a point to keep renting even now.