I dont really buy the issue with "there's no market" just look at the pc market: isnt there are market for convertibles, laptops, tablet+keyboard, different OS, all sorts of sizes... how different is the android phone ecosystem?

There is a market, it is just not lucrative enough for big players to take it.

There is however a company that caters to these niches: Unihertz

The have small phones, massive phones with huge batteries, rugged phones, phones with keyboards,...

From what I have seen, not great on the software side though, and they have entry-level specs, with prices to match. It is a Chinese company.