One important thing you are missing is that you are focusing on a single instance of a single program doing that. These caches are not shared among programs and

One important thing you are missing is that you are focusing on a single instance of a single program doing that. These caches are not shared among programs and unless you are only running a single program at a time in your OS, if every program does such resource abuse (not necessarily this particular type of abuse, but in not caring about resources in general) then you get a slow computer. Computers feel as slow as ever (which was the topic a few nodes above) despite being much faster in theory not because of a single program but because all (or well, the overwhelming majority) the programs in your computer abuse resources - even if a little. It is death from a thousand little abuses.