gRPC shows up when REST starts breaking under its own weight

Picture this: you've got fifteen microservices talking to each other. Each one exposes its own REST API, each one has its own JSON with its own naming conventions, and every time someone changes a field in the payments service, three other teams find out when everything blows up in production. You document with Swagger, but the Swagger goes stale. You write HTTP clients by hand, or generate something with OpenAPI that works "more or less." And when you need service A to ask service B something t