There's also the Lisp philosophy which emphasizes that you are your own libraries' author, too! Third-party libraries can only help you with common business code - anything specific to your domain, or your business, you have to model yourself. Using macros is fundamentally not different than using classes or functions to create an environment[0] where expressing your business logic is straightforward, and invalid states are not representable. Metaprogramming just lets you go further in this direction than "traditional" tools languages offer.

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[0] - The correct term here is Domain-Specific Language, but by now it's badly overloaded and people have knee-jerk reactions to it...