Emacs is, amusingly, a lighter client than most browsers nowadays.
On point, a browser can not remember ifa notebook. Just parse the json. It can also parse text/plain. So, could show the org document without styling. The org document is actually readable. Json... Not so much.
To see the notebook, you have to have a Jupyter setup somewhere.
How is a notebook without proper software to handle it in any way more useful then other structured plaintext-file? Yes, JSON can be prettyprinted in a browser, but what then? It's still a useless mess you can't work with.
Org-mode is great, but you still have to install emacs.