Regardless of the discussion, Electron browsers are very insecure and is not a stable foundation to build a browser on. Electron even recommend that you do not try and build a browser using it.
Also, it kind of makes sense: You'd effectively be implementing a browser (or the GUI thereof) in a browser.
There's also the difference in time between committed patch and end user having a new release in the case of a critical vulnerability, for instance.
Using an embedded browser framework introduces many intermediate parties, some (many?) of which might not have being up to date with the upstream as a priority – which leads to a weakened state of security in the "browsers" downstream.