I guess it is different reasons for different people. But for me, I started using ubuntu in 2005. When I was learning linux, it was just not complete enough. You install another DE/WM, to try it out, and stuff started to break. So I switched pretty quickly. I tried to return every now and then, because it had an environment of newer packages which I waned/needed. But it was never worth it, this or that always broke when you tried to do something peculiar. I use ubuntu every now and then, but it is mostly no good. The issue is really just snap. Snap firefox on rpi, which is the default, is just trash and unusable. It is crazy that they made it the default. I have also had servers where snap-services just eats too much cpu and first thing I have to do is to purge it. So, in summary, I don’t really trust them to provide a reliable system, and I am sceptical of their direction.
Like a fairly realistic one: measurement exclude a cosmological constant as the explanation for cosmic acceleration in favour of a quintessence scenario.