I think it probably depends heavily on the dependency (heh).

Would you reimplement a regex engine yourself? I hope not. Left-pad? Obviously yes. I don't think you can have blanket advice that dependencies should be avoided.

I suspect even quite simple dependencies are still a time saver in the long run. Probably people prefer reimplementing them because writing code is much more fun than updating dependencies, even if it actually takes longer and isn't as good.