I agree that sometimes the best solution is to use existing library, but I can't agree that traversing graphs is "too complex to implement from scratch in a timely fashion".

This very statement reminds me of famous "why can't programmers program" article: https://blog.codinghorror.com/why-cant-programmers-program/

Programming needs some technical skill anyway. And learning "how to use library X" often takes more time than learning "how to implement algorithm X". Libraries are often bloated, bugged, hard to debug or have terrible API. In these moments basic programming skill set is very useful.