It really isn't all that popular these days. It is running on the fumes of history like Windows is. The difference is there is little reason to stay with Ubuntu since it is just Linux.
The stack overflow survey only captures a small portion of the population. It is going to be mostly corporate software development companies.
Ubuntu is still fairly common in the enterprise when it is required by corporate overlords but it is way less popular when users are given a choice. Ubuntu doesn't have much to offer these days and it is riding on inertia.
I have a general philosophy of reinstalling my systems from scratch every few months and honestly Ubuntu is among the easiest for that (Debian is close second, but corporate overlords freak the hell out)