That's true of any large open source project, whether heavily backed by a company or not. You need both users and developers to make a fork successful.
Regardless, though, there's nothing that says the hypothetical developers of a Chromium fork couldn't devote some time to merging reasonable fixes & new features from upstream.
Forking Chrome would be like fighting against Embrace, Extend, Extinguish after you’ve already lost (which we have with Chrome, compared to what KHTML used to be like)