We don't have an answer for this question. All we know is that we are absolutely in love with cats standing up. Why? Because we're biased, and we love every unique thing that cats do, deal with it. And so does Reddit.
Therefore, we'd like to say: thank you, r/CatsStandingUp, for enabling our 'cats are actually humans in cats' bodies' obsession and always purrviding kitties in their most human-like moments for us to admire.