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.
For the most part, iOS does a fantastic job of bringing up old photos I haven’t seen in a long time just on my Home Screen. I can click in, look at a few, think about those times, and then jump to the next thing I was doing. So some weeks it’s looking every day or two while other weeks less.
I agree that most people probably won’t ever look at their grandparents photos, but maybe that’s because they weren’t good photos? Like someone else said, context is important so marking things that happened makes them more valuable.