There's nothing to "fix" - NATS is a distributed and fast pub/sub system. NATS Streaming is actually a client, it uses NATS to communicate and basically just subscribes to some topics, saves messages it receives, and will then replay them back to you if asked.

Imagine how you would build a persistent logging app on top of NATS, and that's what NATS Streaming is.

They did. Partially. I use nats-streaming in Production. It still does not have real “clustering” solution, but for my small scale I’m able to manage ~7-10k messages per second. Which is fine for many companies.