Makes sense as a theoretical problem. Have you ever seen data that suggests it's a practical problem? Seems like one could identify "should be cached forever but wasn't" using etag data in logs.
Facebook did a study about ten years or so back where they placed an image in the browser cache and then they checked how long it was available for… for something like 50% of users it had been evicted within 12hrs
If one of the most popular sites on the web couldn’t keep a resource in cache for long then most other sites have no hope, and that’s before we consider that more people are on mobile these days and so have smaller browser caches than on desktop
Browsers have finite cache sizes… once they’re full the only way to make space to cache more is to evict something even if that entry is marked as immutable or cacheable for ten years
