Why would they ever do an IE6? They don't want to cripple the web as an application platform as MS did but move as much things as possible onto it.
Today when you navigate to google.com from Microsoft Edge, there's a barrage of popups urging you to use Chrome instead.
When Chrome is completely dominant, maybe those popups will be on non-AMP sites urging you to "get the best experience"? It's guaranteed that there will be a lot of internal pressure to use Chrome to promote the goals of other divisions at Google.
Chrome already does this.
And a key UI target for a huge chunk of their applications and services, including search.
If "web browsing" doesn't work in Chrome, that's kind of a big deal for Google.
It only needs to make sense in the minds of a handful of high-level managers, and we all suffer.