This assumes that I could implement something as well as the maintainers of the library I use. I agree that something trivially should be implemented on your own, but if there is special knowledge required (the obvious example is cryptography, but also something like HTTP requests) I rather rely on a widely used library than my own code that I now have to maintain and check for security issues instead of just updating the dependency version whenever a CVE is published.

Also if there is. A client by an API provider for my language, why shouldn't I use it instead of rolling my own?

Another example is a framework like React or Angular or Svelte, which brings along a whole lot of dependencies. Sure, I could not use something like that and write everything from scratch.

But where is the value of all that code to customers? If I want to roll my own HTTP server up from the sockets, I can do that as a play project. But not using libraries for a real world project to solve business needs is a bit of an odd take.

Anyways, that's enough of a rant. Have fun in the replies. 😎