I know many languages, including Swift and Ruby, and I've actually started to prefer modern Javascript. I really enjoy writing ES7 JavaScript with Flow or TypeScript, and everything else in the ecosystem (babel, webpack, yarn, etc.)
I will admit that Swift is a much better language, but I prefer working with modern JavaScript these days.
The point was probably that someone with a good knowledge of one language and little or know knowledge of another favors the one they already know.
There are plenty of people who are quite happy with what they have, and they see no reason to change. Then there are people (thankfully) who are never satisfied and who keep progress rolling.
