>> Why then aren’t people screwing up when using other FP languages such as C#, Clojure, Dart, Elm, Erlang, F#, Julia, Haskell, Scala and Scheme?
First, none of those languages are required when writing for the browser. The author even states later in the article that people are indeed "forced" to use JS.
Second, who says people aren't "screwing up" when using those languages? How would you even know? Badly written JS is often public for the world to see because it's running on the client side. Those other languages are not. How would you even know if people are "screwing up"?