All discussions on the sub must be about events that happened at least 20 years ago (and of course follow the other rules too). But that one is non negotiable.

It matters because everything that happens is part of history, and thus historical. But to keep ourselves from being overwhelmed with modern events -- which the r/news r/politics r/worldnews etc subreddits cover perfectly, we ensure that there is a large gap between the present and the past to maintain something which sets us apart from other subreddits.