It's the hardware
IPv6 is trivial. I've been using in my home network and personal server for years. The only hard part is finding routers that aren't garbage. Even if the router hardware is good, someone is going to load it with firewall rules posted 10 years ago to a message board for "security." Imagine trying to get IPv6 passing through an old government building filled with 5 generations of routers configured by 4 generations of IT staff. Maybe they have a few coax and Cat-3 hops along the way.