Re: "Nobody uses it..."
I use it!
Now, image that you are a really big organisation that's invested a lot of money in the whole IPv4 pit - routers, firewalls, access control measures, all of which are potentially bypassable by a bad IPv6 implementation..
In short, IPv6 is a mess. It's a total camel, designed by people who really, really didn't consider about how it would get implemented in the real world.
And, when those implementation issues became obvious, made it more complicated still.
A pox on it. We need IPv7 - just add another octet at the start of IPv6..
 A camel being a horse designed by a committee. And not a cute itty-bitty-kitty-committee either..