The one thing I gather from that graph is that over weekends, IPv6 use spikes. I assume that this means that networks or devices at companies and schools are lagging behind at using IPv6?
On the other hand, corporations tend not to have the same level of skill, and focus in terms of networking as an ISP, like a Comcast, or an AT&T. Additionally, they're not as incentivized to move everyone to IPv6, because often times, it's easier, cheaper, and more realistic to buy some IPs.
Moving to IPv6 at the office is a difficult project for most, as there is still a ton of enterprise gear that's IPv6-less. Even at that, enabling enterprise applications with IPv6 tends to be a massive nightmare. Lastly, the security implications of IPv6 are not well understood by most people in the corporate environment.
"Google works, so it's not my connection at fault, it must be your site that's broken."
The big reason to support IPv6 now is IMO that (all else being equal) it's better to add v6 support when you roll something out than to introduce it later.
Our network guys seems to love the extra complexity, though.
It sounds easier than it is, the main issue is scaling. Need to connect to one other person for B2B? Trivial. Two? A little harder. Ten, twenty, fifty, ouch...