The point of these services is they're supposed to be an easy-to-use, worry-free photo backup. Amazon/Google/Apple should surely have the resources available to keep my photos stored somewhere with some redundancy. I don't want to worry about how they do it, but that's the idea. In exchange they're probably training image recognition algorithms or what have you on my photos, and I certainly wouldn't keep anything too personal on those services (i.e. nudes). I may even be paying them for more than the free storage limit. The least they can do is be a reliable backup. Yahoo Mail doesn't disappear emails randomly, YouTube doesn't just disappear videos randomly (barring stupid robot moderation). You'd expect the same for your photos on these services.
When I look through my "Watch Later" list, probably 10% of videos are missing. I think you have to choose "show deleted".
I've been planning to set up a script that uses yt-dlp to auto-download the new videos on my Watch Later list every night, but haven't got around to it yet.
