Think of it this way, on the one hand the building changes in value a bit every month. Sometimes it's up, sometimes it's down. And sure, there might be a bank-l

Think of it this way, on the one hand the building changes in value a bit every month. Sometimes it's up, sometimes it's down. And sure, there might be a bank-loan against the building. But buildings are not revalued all the time. They typically revalue when they change hands. You might have it revalued (up) if you want to get a bigger loan, but it's not like the bank is running around revaluing buildings in case they went down. (It's not good for them to acknowledge it's underwater either.) Both parties are optimizing for the _long game_. If the market is in a short-term slump (think < 5 years) then it pays the bank to wait for a recovery, and it pays the company to hang on. Yes, if done at scale, across an industry, then the wheels can come off in a big way (as happened in 2008) but for short term fluctuations there's a polite understanding that it's in everyone's interest to carry on through the downswing into the next upswing.