IpV6 was designed in the late 1990s and early 2000s when no one had any clue what the internet would be like in the future. It’s a pie-in-the-sky design instead of something tested and subjected to the rigors of the real world.
It’s like me attempting to design a product for someone to use in 2045. In other words, pretty much a terrible idea.
This article is also good. IPv6 is a fundamentally bad design that doesn’t deal with any problems we actually have but rather with problems people had in 1995. And that is why it’s been such a failure.