Because you will be excluding connectivity. Maybe you think that only affects far off places and not your stuff and your networks, but be aware that many mobil

Because you will be excluding connectivity. Maybe you think that only affects far off places and not your stuff and your networks, but be aware that many mobile networks are using IPv6. The number of mobile devices keeps increasing. One day you (or the boss) will get a new device and it will have connectivity problems. Google and Facebook will work just fine. Sure there is NAT and various other things carriers and ISPs can do, but that will increasingly be the slow path, and possibly even charged for. You can put your head in the sand, only to have this issue bite you badly and urgently one day, or you can start now slowly but surely making sure everything appropriate is done. For example you can make sure purchases of equipment and software claim to work correctly (how will your VPN work?), do whatever training is necessary etc and gradually add IPv6 to your infrastructure and clients.