Hah!!! I am in the same space. But here is my theory. The human brain (at least most of them) can only hold so much. So, the more you are open to learning and new experiences, the more of the older ones have to be discarded (forgotten).
We have so much knowledge available to us today that not one person can hold it all. Pick and choose.
I remember what is important - or that is what I tell myself.