This has been discussed before, not for a while though. The last time I recall was the first Denver PTG.
In the past we did remove docs as branches were EOLd which resulted in lots of 404s as a search engine would index a page and return it but we had removed it so the user got a 404.
There was also a lengthy discussion about not removing docs that people are using. I haven't looked at the user survey results but I'm sure you've seen the long tail of people still using very old results.
We could potentially remove the older releases from the index by doing something similar to the crossplane project did. That has the potential to solve most of the problems we've all seen but doesn't remove the docs for older releases in general.