Dependencies aren't free. If you have a library that has less than a thousand lines of code total that is really janky. Sometimes it makes sense like PicoHTTPParser but it often doesn't.
Not saying left pad is a good idea; I’m not a Javascript programmer, but my impression has always been that it desperately needs something along the lines of boost/apache commons etc.
EDIT: I do wonder if some of the enthusiastic acceptance of this stuff is down to the extreme terribleness of the javascript ecosystem, tbh. LLM output may actually beat leftpad (beyond the security issues and the absurdity of having a library specifically to left pad things, it at least used to be rather badly implemented), but a more robust library ecosystem, as exists for pretty much all other languages, not so much.
Left-pad isn't a success story to be reproduced.