Chrome being open source and free seems like a significant difference.

Technically Chrome isn't open source, Chromium is and there are differences mostly related to Google services and branding.

* As far as we all know. *

This relationship means that Google can be throwing whatever they wanted into Chrome, and not necessarily have it make its way into Chromium.

VS Code is the same way, and a lot of forks are finding out about that relationship right now when Microsoft blocked their C++ extensions from running on anything other than the proprietary build.