What surprises me is that no one has made a phone case that integrates a flip or slide keyboard. It would be an easy way to add an aftermarket physical board to a phone, and from these threads it's clear there's at least some demand. I understand it's probably not enough demand for a whole phone line, but surely something like that would be possible.

When I lived in Japan I had a lovely flip phone with a nice big screen (for the time), no thicker than my cased pixel phone now when closed. The only clamshells that are left have comically tiny screens and are thicker than a fully loaded wallet. They're substantially less functional than what I used in 2007. It's bizarre.