Its incompatible with IP v4, has a stupid addressing scheme, it requires new router hardware and software for isps to buy and nobody is using it because of all the aforementioned issues.
And by "stupid addressing scheme" do you mean it's too big, or what? You can ignore all that stuff with mac addresses and make all your addresses go like prefix:subnet::1 prefix:subnet::2 prefix:subnet::3 if you want to.
Screw DNS. Screw the recommendation to stay away from IP's. If it's important enough to be on the network, it's important enough to have a static IP.