I'm surprised no one has linked to these two articles by @apenwarr yet, I consider them "the bible" for understanding IPv6 and why it was designed and implemented the way it was.

- The world in which IPv6 was a good design: https://apenwarr.ca/log/20170810

- IPv4, IPv6, and a sudden change in attitude: https://apenwarr.ca/log/20200708