Well alright I see where you're coming from you know someone using something that they're happy with and have no reason to switch ought to be left alone, but still "sell linux" in this context is just provide information about why people use it at all and with that information some people might decide to use it.

I also kinda want to add, that using something different from the crowd has a social stigma that comes with it when they send you a file or expect you to install an application that your OS just doesn't have. So some people do feel a need to sell linux so that their lives are easier and don't have to deal with incompatibility as often.

Which is why as much as I hate apple, I'm kinda happy about Mac having such a strong userbase, because the expectation that you have a windows machine can be removed from social stigma.