I made a similar point about Gundam that someone mentioned: just because we listen/watch/read something that was old doesn’t mean all old things get listened to/watched/read.
We listen to some centuries old music, but there was a ton of music that’s centuries old that have been lost to time. There are a ton of lost works, things we can assume exist because they were referenced but we have no surviving copies of them. Specifically in the case of classical music, we only really listen to the stuff that was lucky enough or considered good enough to be saved. Even from the composers we listen to nowadays, we don’t have all of their work: consider how much of Bach’s works are just gone, referenced but with no surviving copies of the music anywhere.
The Rambling about how we don't actually listen to all the music from 50 years ago, we listen to the music that was popular enough to survive in culture for 50 years.
And even without considering lost works, think about something like a radio station, and how it’s going to tend to play the most popular songs for whatever genre the station is. Think about all the songs that came out in 1973. There were hundreds of them. There were hundreds of albums released. But we don’t listen to all of those songs and albums. People still listen to Elton John and Pink Floyd, but society doesn’t really mention The Carpenters anymore.
If you look at books, songs, shows, movies, etc., you’ll see that tons of stuff gets made all the time, but a lot of it fades out of relevancy quickly enough. Even Wikipedia lists 174 movies to come out in America alone in 1973 (IMDB lists over 3,300 movies worldwide.) Some were big like The Exorcist. But what about Jory, The Neptune Factor, and Lolly-Madonna XXX? We’ve still got copies of them around, sure, but they aren’t really influencing anything.
The whole point is that while things from 50 years ago might still have cultural impact, it doesn’t mean everything that came out 50 years ago is definitely going to have a cultural impact, or that everything made now is going to still be relevant 50 years from now. While it’s not impossible for people 50 years from now to still love OPM, the odds of any one thing still being relevant isn’t that high. Star Wars and The Goodbye Girl both came out in the same year. One of those is still getting movies made and is worth $70 billion. One of them got to be played as background footage for the live action adaptation of a video game.
I feel like I’m rambling a bit, and this also doesn’t touch on the idea that crossovers can water down the identity of the thing they’re put in, but the TL;DR point of it all is that just because something might be popular 50 years from now is by no means a guarantee, and doesn’t get around the fact that taking something that’s currently popular and putting it in a setting that’s 50+ years from now is clearly pandering.