It’s top down for same reason things are generally left to righ. In the days of ink and paper, you’d end up with a smeared mess - ask a lefty what a pain in the ass that is.
Less of an issue nowadays of course. Still the very idea is a bit nails on a chalkboard to me, but I’m old and wondering if it’s a generational thing. Maybe you feel like this since many interfaces push text entry to the bottom?
Reality has become indistinguishable from satire.