The thing about TIHI, interestingasfuck, SLPT are that they regularly made r/all. Content hitting the front page means views for Reddit. So it's less about the sub's specific userbase, and more that those "main" subs have broad user appeal that brings people to Reddit in the first place.
And currently they're all shuttered. Which means less content on r/all, which decreases the general audience appeal of Reddit.