Remember when people kept justifying Android over Windows Phone/Maemo/WebOS/BlackBerry/FirefoxOS on the grounds that it was free and open source software, infinitely customizable, and that Google was a good-faith partner who wanted openness in the mobile market?
Good times, good times.
AOSP is still open. The problem is nobody wants to bear the (monumental) cost of polishing and convincing brands to allow installing it in THEIR devices. Google was motivated back then for creating an alternative and openness was a good bait.