Linux is the most used operating system in the world. You probably use Linux every day. Android is Linux.

Linux can be pre-installed and it can be as simple to install for a user as windows. It can also be used without the terminal or anything else. All this just depends on which distro you use. Thats the biggest pain point for new people. They think Linux is one thing, but there are so many ways Linux can be customized and used. Finding the right one is hard, especially if you don't want to touch it and let it handle itself.