I think it may be fairer to say, “most people pick up JSON because of the flexibility.” Those who continue to use it for anything where there’s a consumer of your API probably do come to want types. In my day job I am starting to enforce end-to-end typing as best I can (given it’s Python and JSON) because our payloads are partially content from agents and I want to be able to flag up weird shit if we can. Certainly not the only gate that we have for looking for prompt injection and not even a great one, but it provides some piece of mind.