It's the only language allowed in the browser as a "first class citizen". WASM lets you use other languages now, with a performance penalty for accessing the DOM.
This creates a situation where loads of developers are forced to use it despite the deficiencies and weirdnesses which cause problems in large applications - but other developers see those as features for small simple uses of Javascript.
This creates a situation where loads of developers are forced to use it despite the deficiencies and weirdnesses which cause problems in large applications - but other developers see those as features for small simple uses of Javascript.
See also https://www.destroyallsoftware.com/talks/wat