Mainstream doesn't use Linux because of no gaming ecosystem. There have been some attempts at getting games running, but for average user it seems too limited. Still in 2020 the Linux desktop experience isn't smooth - you often need to dig into configuration files and it is too easy to mess it up. Then you have Google purposefully turning off GPU acceleration in Chrome so people think that Linux is just slower than Windows. I think Linux is missing proper UX team dedicated to making basic user problems easy to solve without the need of PhD in computer science.