Latency, for one. "Microservice" means reaching out over the network to perform an action, not necessarily: make an HTTP connection, transfer JSON, receive JSON back and deserialize. Microservices can just as readily be performed via protocol buffers or Thrift over ZeroMQ, raw TCP/UDP, etc.
You are correct, but missing a larger point: the ecosystem backing JSON-over-HTTP is large and expansive, and as a result development for apps built on that technology has effectively been commoditized.
0) In the late 1990's to early 2000's, exactly the same thing would have been said about XML. And yet, here we are...
1) So, you're saying that the fact that you can hire college freshman to complete your project outweighs the issues introduced by using the wrong tool for the job?
0) technologies evolve over time. JSON-over-HTTP will be supplanted by something, eventually, which almost certainly will also be something that acts to commoditize labor
