Some novelties are newer than others. Those you remember best are those that don't fit with your generalizations about the world. As you grow older your generalizations get better and less things surprise you. The more you've seen, the more generalizations you need, because you don't have time to review the whole of your experience everytime you take a decision. The generalizations become a gut feeling, you know how to react but you forget why. The gut feeling makes you more efficient but by unconsciously generalizing from what you perceive you lose sight of the details. If this explanation is correct, there must be ways to reverse the process, at least for some events. Try meditation maybe, or drugs? I haven't. Tell me if it works.

On the other hand it might just be your memory getting worse at recording new things, because your brain gets old and no longer works so well.

Or maybe your brain is becoming more careful about what it records because there's not as much free space as there used to be.

Or maybe your brain is just bored, at first it really loved this shiny new recording thing and played with it the whole day, but then got used to it. Nowadays it only gets it out for the really big occasions.

Anyway, this is really about the pace at which you record informations, and about the amount of informations you discard. I'm sure these questions also arise in algorithms or machine learning. Certainly some knowledgable scientist on this forum is going to point out a parallel with some machine learning algorithm or information processing theorem?