One reason most people prefer Windows over most any OS, is gaming in general and the fact that Windows, though not necessarily easy to use, is what most people are used to using and is in turn more user friendly and easily supported and easy to get help for. It is also well marketed obviously, as every computer except Apple brand computers have a Windows OS. So it's just a matter of what people are used too and programs it runs.
Where as Linux just doesn't support certain formats and programs that most people who use Windows need, it also is fairly difficult to use especially after using Windows for most of one's life and just switching. I'm not new to Ubuntu, but I am just now starting to fluidly use it and there is a lot of learning to do upon switching to a Linux OS especially learning Terminal commands and some people are just lazy, or don't have the time to learn it.
Personally I love Ubuntu, I am fluid user of Mac OSX and Windows and now Ubuntu as well. Out of all three I have specific things I need. I use windows for gaming mostly, not much else, simply cause it is the most supported platform for PC gaming. I use OSX for multimedia and development because in my opinion it works amazingly. Ubuntu I use for my on the go coding and for school, being that Libre Office is free and college is expensive enough as is.
Mostly it's a preference thing though. It depends on what you as a user are trying to do on a computer that makes one OS the truly better than the other. I hold all 3 of them to being highly useful. The concept of Ubuntu being open source, since it is a Linux Distro, to me is just fantastic. It does have it's flaws equally though. Hence why there's a big ask forum for users to get help as there can be many difficulties with installing drivers and GRUB etc. So support, program platform, and preference is what would make a user prefer one to the other.