There's a difference between "adding a style checker yourself" (or the project owners doing it, if it's not your project) and "having a style checker built into the core tools that yells at you unless you either conform, or turn it off in every single project you write".
Sure, C# convention for the standard APIs and whatnot may be PascalCase, Java camelCase, and whatever. But that doesn't mean that Everyone Must Follow The Standard Convention. That way lies Python and frankly, Python's "there is One Correct Way to do everything" culture really turns me off.
But even Python doesn't do this. Neither does Java. Yeah your IDE might, but that's a weird IDE feature then. And we can just use a different IDE. You can't just a) use a different compiler and b) tell everyone who's interested in your project to use the different compiler or ignore the warnings, they're spurious trust me bro.