For me personally it’s unfamiliarity. Technically all my devices and networks use IPv6. But I just enabled it in my router and used my hosting company’s configuration.

But one of my servers at home should be reachable from the internet but that is only through IPv4. Configuring port forwarding through my router was intuitive and straight forward. But for IPv6 I have to allow the port to be open, but I don’t want it to be the standard port so I have to configure the corresponding service on the machine itself to listen with a specific port on a specific address. But I have no idea what each of the addresses it has mean.

I think some of them are purely internal, some temporary, some less so. And if I ever found out what to use I would then have to configure ms DynDNS, which is currently just pointing to the public IPv6 address of my router but not to the server I would want to reach.

I could learn all these things. But I just can’t be bothered because the IPv4 stuff still works.