There is an explanation in the README file, but I'll explain: It helps to standardize workflows across a number of different source repositories (all Go based)

There is an explanation in the README file, but I'll explain: It helps to standardize workflows across a number of different source repositories (all Go based), where a number of different developers had come up with different ad-hoc ways of generating code against protobuf definitions. Since the syntax is Go-derived, it reduces cognitive load for developers when specifying protocol buffer definitions. We understand that it may not be for everyone, but it works for our team.