You'll be surprised how well it works by just switching the user-agent. It's more of a "too lazy to make sure it works" than a "actually doesn't work and Chrome should be used" situation.

Too lazy to test probably. If you support IE, Safari, Chrome both on the desktop and mobile, chances are that your site supports practically everything.

Unfortunately, often giving the official thumbs up requires passing some test suite. If companies have gotten better with their development methodology, their testing methodology is still often "Take a bunch of guys in India and have then run through that extensive check list".