A woodworker would have more off the shelf tools if they were equivalently cheap/good/fast/efficient as a custom tool. Physical objects can’t be so freely copied as a software library.

I do agree fully that programmers should strive to understand every layer, and building your own tools is a great way to get experience that helps with that. Yes, left-pad is unnecessarily granular abstraction. However, in each domain, we inevitably depend on other software, and that breadth of that graph is part of the reason for why you can accomplish so much with so few people writing software.