[k__]

The JavaScript ecosystem exploded in the last 5 years.

JavaScript developers weren't aware of what adding static typing could bring them and there was so much other stuff happening. Also, because JavaScript grew substantially in these years, many new devs joined and they had enough to do with learning JS.

Then CoffeeScript and later ES2015 came.

Many statically typed languages are able to compile to JS: Scala, Nim, Rust, Kotlin, Clojoure, Dart, OCaml/Reason.

Facebook even tries to add typing directly into JavaScript with Flow, which can even work with comments, so you aren't forced to run it through a special compiler before bundling.