The post isn't "Why did people want IPv6" but "Why is IPv6 such a complicated mess compared to IPv4? Wouldn't it be better if it had just been IPv4 with more address bits?"
Actually, IPv6 is good design. Adoption is slow because most people and companies always prefer a cheap short term inferior solution compared to the good long term one.
Now, IPv6 is 25% of traffic. It will continue to grow, and at a point the network effect will be on IPv6 side. Not long after that, IPv4 will only be a niche for a few legacy systems.
(What about percentage of overall traffic on the internet? That's much harder to measure, but you'd expect it to be something like the product of 25% and 50-70%. But that particular stat isn't actually very interesting; percentage of clients and percentage of servers/traffic are a lot more useful.)
Because it was designed by a committee?
My guess is what you consider unused complexity is just something you don't see/deal with on a day to day basis so you wonder why it's there. This doesn't make it useless/inefficient it just means you don't use it (or don't interact with it directly even if it is used somewhere in the network path)
In hardware, if you can reasonably foresee the need for some feature in the future (where "future" could even be > 10 years), and adding it now doesn't blow out your cost budget, you should probably add it.
The cost of being wrong in the direction of excess complexity is higher than the cost of being wrong the other way. Layers are added, never removed. A deficiency can be fixed by adding something. A misfeature or ugly hack is a boat anchor we lug around for eternity.