It makes no sense from an usability point of view

It's like insisting on a steering wheel for a plane.

Different means of interaction and limitations and use cases require different interfaces.

Also the "Ubuntu on the phone thing", it seems they were doing it because of the wrong reasons (mainly "We like Linux") rather than focusing on the user and the ecosystem

Why should we all have to buy another completely separate computer if we want to use a mouse/keyboard/monitor, when we already have phones?