The cameras that people have on their homes are not necessarily places that they are at on a regular basis. Some homes are vacant, some are secondary homes, some are vacation homes, some are rentals, etc.
I've had a couple failures over the past ~decade and it has never been "mysterious". If you don't panic and use context clues, there is always plenty of information. Pretty much any foreseeable urgent problem resulting in a failure would have produced some footage that indicates the issue. And non-urgent problems that result in failure are easy to detect. (e.g. if your UPS sends you an on-battery alert, and 5 minutes later your cameras fail, you just had a power outage)
The only time that cameras go black without warning and it is warranted to panic is when you're the comic relief character in a bad horror movie.
