Macros definitely do not make code generation trivial. Rather, macros make code generation that should be trivial trivial, but generating (say) serializer/deserializer does not become trivial.

It could be that macros are too low-level for the serializer/deserializer case. What you really want is a definition of the thing to be (de)serialized in some language and two different translations of the same definition. The translator might need to make multiple passes over the same definition in the course of even a single translation.

Another case that illustrates this point: Suppose you are defining a wire protocol between two communicating processes. The tool you want is a language in which the protocol is defined, from which sender and receiver code can be generated. A flexible tool would be able to generate sender and receiver in different languages, or, in fact, in multiple languages. It would be able to generate language-independent documentation of the protocol in multiple formats. It's not easy to see how macros embedded in a single programming language could produce these results.