Well, change has high costs, that's why. So the benefits need to be big as well. I think the issue for Python 3 is the benefits weren't that large compared to t

Well, change has high costs, that's why. So the benefits need to be big as well. I think the issue for Python 3 is the benefits weren't that large compared to the costs, and for IPv6 it's the same, albeit people know that the cost/benefit ratio changes over time as IPv4 gets more and more overloaded.