I think this is how it went down:
Management: "OMG Bill isn't here anymore and Windows 8 pre-alpha is crashing constantly.. what can we do??"
MS Intern #1: "Let's just dumb down the graphics like Windows Phone and there's less processing involved and we can dedicate that to system resources instead, thus less crashing..."
MS Intern #2: "I second that, what a fantastic Idea.. we can give it a catchy name like Metro, what do you think Mr. Nadella?"
Nadella: "Brilliant, can we make it so people have to sign in with a cloud based Microsoft account so we can track them even when they log into Windows?"