There is nothing preventing anyone to build a whole new set of infrastructure for such "binary first serialization" 20 years ago, 10 years ago or today. We don't even need to do that much. Instead of "text/html" or "application/json", let's just use some binary format in the request headers everywhere and make both the client and server support it. Why hasn't that happened?
It's for the same set of reasons, and people aren't dumb.
It's for the same set of reasons, and people aren't dumb.