It’s just a question of funding. Ubuntu made a push for mobile years ago. They put up a phone on Indiegogo, but it didn’t hit its funding goal.

https://en.wikipedia.org/wiki/Ubuntu_Edge

This is what their Unity Desktop was for as well. A desktop environment that had a consistent design language from desktop to mobile.

The remnants of all of this are still kicking around, I think the community still maintains the phone OS, but without the weight of Canonical really pushing it, and a phone shipping with the OS pre-installed, it won’t get as far.