It used to be you could find a box of photos or keepsakes that you inherited to look back on how things were or when you were a kid. Now, most of that is stored on phones, and most parents probably don’t think to share or save them in a way to be passed down in the future.
How many pictures are lost because nobody ever looks at any of the 1000000 pictures they’ve taken?
I think you are right, they are all stored somewhere and might even have back-up. But at some point of time it will be way to many photos to go through in order to pick those that are worth saving. And then all photos might be deleted/lost.