Or left it with friends or gave it to a roomie or they were in a furnished apartment or had an important assignment in temporary lodging that's now ended or are keeping their apartment but moving elsewhere for a few months. There are probably lots more reasons. I agree with you. People travel for many reasons and it doesn't mean they'll be gone forever.
If something happened to me or my wife (unrelated to virus), we'd probably travel to where one of the kids live so we'd have some support. Empty the fridge, lock up the house and move there for a few months or one of the kids would move here to help us, doing the same with their place.
I agree wholeheartedly with you. There is a case for necessary travel intercity.