You say this matter of factly and yet I've seen countless people talk about using termux more than a desktop shell.

Maybe iPhone is different but most phones you can connect a keyboard to, making the shell pretty usable. Not my cup of tea but I have tried it. I'm still holding out on the dream that a good Linux phone might exist one day.

In the grand scheme of things very little people use Termux on Android out of the billions of people who use Android. Additionally Termux's design is not aligned with Android's app model which has caused many headaches for them. Trying to force a terminal to exist on a phone is possible but it is being forced and is not a natural product that would exist if one was trying to design the best user experience.