I've always thought of protobuf as a Java thing.

It worked great in Java, but not so well in JS, especially with Kafka.

Protobuf was never particularly a Java thing. You could more accurately say it was a C++ thing. It was initially developed in C++, and used mainly in C++ services at Google. The implementation and early ecosystem were C++-centric.

Later, Go became one of the major Protobuf ecosystems, and today it would be understandable to think it was a Go thing.