Streaming JSON is troublesome because the base object is unbounded. It's true that there are workhorses that handle this, but when debugging responses, ad hoc tooling is very useful. If you can't examine a response without using a streaming parser, the cost of maintenance goes up significantly.

It's important to remember why we use JSON. It's not because it's well suited to transmission. It's because it's easy to reason about. If you want to move to a streaming format that is not easy to reason about, you may as well move to a binary format.