This loss isn't recognized unless you sell. If your house loses value but nothing else in your life has changed then "Just keep swimming" and historically you will win in the long term.
Maybe on aggregate but the devil here is in the details.
Plenty of people buy houses in "on the rise" areas and reap the benefits as desirability increases, it's true. Even market crashes like in the mid/late 00s don't impact their long term prospects. But there are also dilapidated cities and small towns in this country that have fallen from their heights never to recover.
It's easy to look back after owning your home for a decade and conclude it was all inevitable, but the "home ownership" bet is one that the house you're buying in will be in a desirable area in the future. This isn't always going to be true, and it's a real risk.
And yes there are protections from being on the hook for the full levaraged amount. You can walk away from an underwater mortgage, but if you put in a large down payment you're kissing that goodbye, and it's still a pretty big disruption in your life even if it's one you can recover from.
I was in that situation and probably on paper we should have walked from an underwater house. But we could afford the payment, so we stayed.
The only really annoying thing was waiting ten years until the value went back up enough that we could refinance from the relatively high rates we had been paying. Annoying to be paying 8% when you could get 3% but you can’t refinance because you don’t have the cash to become not underwater.
This loss isn't recognized unless you sell. If your house loses value but nothing else in your life has changed then "Just keep swimming" and historically you will win in the long term.