Safari can probably be discounted since Apple discontinued the Windows version in 2012. A browser that can only run on 18% of desktops worldwide isn't necessarily the competitor Google is looking for.

Edge is available on Linux and macOS, so it would probably do. But that would allow one of Google's biggest competitors to drop an under-performing product and lobby for antitrust against Google. Unlikely to happen, but a risk Google might not want to take.

https://gs.statcounter.com/os-market-share/desktop/worldwide