You think it'll always be there, and next thing you know it's still there, but you aren't.
I think this is just One Of Those Things. Growing up, I did all the Smithsonian museums on class field trips, but never on my own as a teen/young adult. Living in NYC now, I never visit any of the museums unless there are people in town who want to go. We have been making an effort to see more theatre, but it's so darned expensive that we only make it two or three times a year at most. (Broadway theatre, I mean -- we see everything my sister's company does, and part of their philosophy is that cheap tickets != cheap theatre, so they always price their shows less than the cost of a movie ticket.)