IPv4 should just go away already. Linux, Mac, and WinDOS had had IPV6 forever. Whatever doesn't support IPv6 should just go away as well. All that old shit is hackable virus prone garbage anyway.
The problem is that numerous companies haven't invested the time or money in ensuring their network can speak IPv6 or to the IPv6 world. The main issue has probably been that it was cheaper to do business a usual. Until major services do an IPv4 blackout day or ARIN raises the prices of the remaining IPv6, companies will be dragging their feet.
One site amongst the feet draggers is