CO and button are the most profitable positions in poker, so naturally the range of playable cards there is wider. And if you think about it logically... you are in the CO, there is only button that has position over you. While you're raising yourself, you narrow the range the button will have to raise or call themselves. So it's only natural that game is evolving in that direction.
I'd predict that in the future things will get even more loose, until we hit the breaking point where those "more daring" players will start losing more than winning. Then the meta will very slowly shift back into more tight direction. Same happens not just in poker, but other games with concept of risk vs reward.
So in short, people must have realized that it's widening the range on CO in profitable at this moment, so they are doing it.