If Linux ever really gained mainstream appeal (say 40-60% adoption) it would be ruined by many of the pressures which ruined most mainstream operating systems. I think we’re far better off with Linux at 1% or so.
I think Linux is different than other operating systems because if something goes mainstream that you don't like you have tons of viable options. With each component of the OS being tweakable you can choose opinions that others have made or forge your own path.
For example if you don't like whatever the latest window manager is you can pretty easily replace it with i3, bspwm or any other window manager that you prefer. Want a different desktop environment? Great, there's plenty of them. Prefer the ethos or core values of one distro over another? Sounds good, I'm sure you'll find something you like.
It also makes troubleshooting a lot more difficult, since any efforts to find solutions will invariably land me in posts primarily about some other combination of components and it's up to me to sort out their relevance to my issue.