Specifically, for callbacks, where a lexical this was needed. Regular functions don't need shorter syntax, and this-sensitive functions are pretty out of vogue anyways.
See:
- https://esdiscuss.org/topic/unbound-arrow-functions#content-6
- https://esdiscuss.org/topic/expression-closures-as-compliment-to-arrow-functions#content-13
- https://es.discourse.group/t/shorthand-for-inline-functions/926
- https://esdiscuss.org/topic/arrow-syntax-unnecessary-and-the-idea-that-function-is-too-long
- https://esdiscuss.org/topic/automatically-binding-extracted-methods#content-6
- https://esdiscuss.org/topic/the-tragedy-of-the-common-lisp-or-why-large-languages-explode-was-revive-let-blocks