I understand why pages disappear. I'm just saying the expecting a search engine to return a result from 5 years ago is kind of a bad metric to be using in whatever point was attempting to be made.

I don't want results to be dropped arbitrarily. It kills all of the good content. I don't need a book to change every week to remain relevant.

edit: and to directly address what you said, excusing a search engine's loss of content because sites have disappeared because the search engine dropped them is circular.