But those libraries often have parameters, switches, hints, and secret knowledge of the type "do not solve problem X by doing Y because although it seems okay on the surface, the implementational details will increase the complexity from O(N) to O(N^2); use this trick instead".

So we use libraries to solve the problems, but we also need years of experience using those libraries, or we easily create problems we didn't expect. Often there are many alternative libraries for the same task, and the library-specific knowledge becomes obsolete in later version.