Linux is wonderful and works plenty fine, but as a civilization we are not ready. There's still so much that won't work out of the box, for most manufacturers it's an after thought if any at all.
You can't walk into your avg store and be like I want a computer with Linux that will play fortnite.
You can't blindly buy a video game or a multifunctional printer without serious consideration.
Unlike Windows where it's the established norm that it will work 100% of the time.
Sure you can argue that a user should just learn to deal with that and teach themselves how to install Linux and cope with whatever comes up.
But that's just unfair to grandma and anyone else that hasn't made computers a hobby.