I think the answer to the question is actually there are quite a few modal text editors that aren't forks of vi/vim. However they all use the vi key bindings. Vi users get the key bindings into their muscle memory so relearning a different set of key bindings would be really hard, so no-one would create a different set of key bindings.
But lots of different editors have re-implemented the vi key bindings from scratch. Just look at this question about IDEs with vi key bindings. At least half of the answers are editors built from scratch that implement vi key bindings, not versions of vi embedded.
