Earlier quoted context omitted.
> Microsoft would fork it within hours and everyone would switch their upstream to Edgium. Why would people trust Microsoft more than Google, though? Even with really bad actions, switching browsers is very difficult (i.e. it requires making an active choice and change about an obscure topic) and I don't see normal people doing it, which is what would be required for this to happen. Microsoft can't get any traction f…
Edge solely exists to keep the Windows OS bundled with their own browser. My 70 year old mother doesn't want the faff of installing Firefox so Edge fits the bill. It provides for her, her needs. I've installed Firefox and it sits untouched. Microsoft doesn't care if people use it or not. It's easier and cheaper for them to integrate as Chromium does than it is to upkeep Trident. It's not their business too. My take t…
I don't have any more insight than any other commenter, but in my estimation a major factor is how practical the browser is to fork. By the time Microsoft switched to a Chromium base for edge, creating and maintaining a Chromium fork with meaningfully different UI was fairly well-trodden ground because it had been done several times already, whereas almost nobody had forked Firefox (except for toggle some flags or keep the UI frozen in time). The one countervailing example, Brave, also switched to Chromium for similar reasons.
Additionally, this was the beginning of the arc of working overtime to court web developers that it's still in the midst of. By shuttering Chakra (the old Edge rendering engine) and switching to Blink, Microsoft improved its reputation with web devs.