The early rising part of the population would love to pull that off, just like it actually happened for centuries now. The problem is that late rising part of the population has never disappeared and does have a voice. Late risers can't do anything with people collectively deciding to open work time at 7 or whatever. But they can and will voice their opinion when a public discussion about time zone will inevitably arise. Surprise, surprise, late risers exist, and they are also human.

PS: by late risers I of course mean people with shifted circadian clock, and not "lazy" people, like they are sometimes presented.