I've been wondering the same. Apparently, where I live (HCOL) people don't care about ever paying off the full amount, as long as the monthly installment is low. Regulations only require that you paid off 33% of the house value after 15 years.

You do need to start at 20% capitalization though, which at current prices means they need to own assets already (market risk), or have bonkers amounts of currency sitting around (inflation risk). I understand the FOMO some people must have.

I wonder if ultimately there is a cascade happening, where increased valuations lead previous owners to either take new mortgages, or sell their old house, and pay more for a new one. Which creates a cycle of ever increasing prices? I've never read anything though whether such an effect exists.