I feel like crypto is an outlier; you should definitely use well-vetted libraries for that for a whole plethora of reasons.
However, I think the reason that people got upset over the left-pad thing was because it was a library that most engineers could write fairly easily, without adding in another failure point.
If you rely on the the language/platform's built-in libraries, typically the amount of wheel-reinventing you are doing boils down to writing simple wrappers, without adding in another external point of failure. These libraries are typically more production-hardened than something you'd find on NPM or Maven or Nuget.