The promise of Protobuf/gRPC for seamless communication across tech stacks just wasn't delivered. Third party projects like Buf or BetterProto for Python try their best but it's still a nightmare trying to integrate with gRPC from something remotely modern, like Python with uv and async/await. Plus there's a lot of little pains like not being human-readable, always requiring HTTP/2 and thus HTTPS, and so on.

JSON isn't "optimal" but after transfer compression it's not that bad, and the support for JSON Schema is much better across the stacks I use, e.g. Zod in JS/TS, Pydantic in Python, etc. And it's fully usable "by hand" without having the schema, for one-off scripts and such -- compare with Protobuf where you need the full definition to even parse a chunk of data.