Most of these smartphones and tablets have homescreens which serve a pretty similar purpose. And people are used to having links to all their favorite apps on it.

Yeah, but I've yet to see somebody to be productive on those.

Either the setup is too limitating : trying to do anything multi task on a phone OS is excuciating, you can't have your 3D rendering software/IDE/veracrypt/... installed in chrome OS, you don't have enough hard drive space,

Or on the other end of the spectrum, I even got friends who are minimalistic, they have no windows decoration, all is keyboard based, with an arch and dvorak layout, doing everything in VIM. Well in the end, they are slower, because they have to keep so many things in their head to do the most basic thing. Like 70 keyboard shorcut (on 3 different keyboard in case they are not on their perfect seup) layout and the position/index of their windows and names of files to just edit + switch. You can literally see them think before every action that requires context switching, which is brain power that they don't use for fixing the problem. And by the way, they spend a lot of time taking care of that setup, despite the fact they advertise it as rock solid.

>Smartphones, tablets, and Chromebooks are incredibly popular and lack a desktop.

Are you suggesting that Ubuntu should follow smartphones, tablets and Chromebooks in not providing the user a way to access the local file system?