Not surprising. They haven't mentioned it for months. I assume they want users to use the in-app browser instead.

Was nobody using it?

I was not even aware that there is a browser, actually. Though the idea is great, dozen of designers already on their way to create hardware for AI, specialized for AI. Does not Jonny Ive (ex apple designer) working on hardware for OpenAI currently, too? I would not be suprised about another browser or even OS for it.