For language designers I point out in my other comment that Anders authored both C# and TS. TS' influence on ES6 is documented publicly.. heck TC39 has an open proposal to add type annotations to JS now!

As for users, any dev that touches frontend has to write JS, unless you're purely a mobile or desktop shop (even then, there's electron). So yes, I think tons of folks willingly write C# and JS/TS. I'm certainly one (though write more Python than both these days). Was I an early adopter of async in Python because of my familiarity of it in C#/JS? You bet I was. Maybe I'm "insane."