I realize the OP is about IPv6 but my comment puts the blame on operating systems. Between the operating system running on the server, through the routers of the internet and a user’s home router, through the consumer operating system running on the user’s laptop, and all of the firmware and microcode along the way, there are many, many more layers involved what is specified in the OSI model.

And so many of these layers exist for legacy reasons, business expedience, and market failure. They don’t actually make things better.