[Spooky23]

Bankrupt condo associations and people with underwater mortgages walking away. For the rental units, the profits tank, so the landlords tighten the screws on opex, and they aren't "luxury" anymore.

You may recall 2008, when this phenomena happened with single-family homes. Condos are much more fickle investments.

[Scarblac]

Note that in the Netherlands you can't just "walk away" from a mortgage. If the bank sells your house and the yield isn't enough to pay for the mortgage, you're still on the hook for the rest.

After 2008 the housing market just more or less closed down. Nobody was selling as their mortgage was under water, so they just stayed where they were.