[heyyyouu]

It has nothing to do with AMP. There's a lot of reasons why, but one reason is for example, two different sites can technically be hosted on www. and the non-www version, if the site isn't set up to redirect the www to the non-www, for example. So this could, in certain scenarios, pose a security risk in that if you pretend that www and the non www are the same sites -- when they're not -- it can make it easier for those that hijack one or the other to get away with it. Now, that's fairly extreme and esoteric. But there are actually times in development when you use subdomains, which this makes more difficult, and there's other subdomains they're considering trivial which, in fact, aren't. This is really good discussion on the topic and why this change just simply ignores so many technical issues, best practices and simply realities: https://bugs.chromium.org/p/chromium/issues/detail?id=881410