Who determines what is culturally relevant?
You’re saying that if I make my own movie with my own funding and time/effort, if enough people like it and the culturally relevant switch gets flipped on they get to take it from me while I’m still alive and I don’t have any say on whether my work is duplicated or screened?
What if I run a SaaS product, people have been using it for 30 years, and they’ve determined it to be culturally relevant. Do they get to copy my source code and run it for themselves?
These are 70s and 80s movies. Many of those who contributed to them are still alive. It’s entirely reasonable for those people to determine how/whether to distribute their own art.
If you believe in that level of public ownership I can respect that you hold that opinion, but I don’t agree with it. At the same time, I do believe that copyrights expiring a lifetime after the creator dies are unreasonable.
To me, the right balance of copyright law is somewhere in between the extremes of Mickey Mouse ownership in perpetuity and complete public ownership.