Ubuntu has already accomplished the year of linux on the desktop many years ago. Ubuntu is a good platform for development, for doing office work and even for gaming it's ok now with steam. Unless you're really dependent of a small fraction of things you can't really do on linux, it's been a pretty for many years already.

The second point is about popularity. Who still uses a desktop? Normal people now do most of their stuff on smartphones, tablets or consoles, desktop is that boring thing used only for work in your office. The desktop died before linux becoming popular, that's the reality.