[1]: https://news.ycombinator.com/item?id=37549745
There are plenty of possibilities I could guess but only dang (Daniel) would know the official answer. If he gives you the official answer please share it here. hn@ycombinator.com
There's lots of reasons why it's a good idea to host services on v6 and v4, but most of them aren't terribly important for a text only forum with limited audience when the facility doesn't support it.
That said, a quick look seems to indicate that v6 is an option at their facility now, so it might be more feasible now.
My take: IPv6 Internet is a second class network. IPv6 doesn't really hold any value unless you're somehow bridged to the actual IPv4 Internet. So why bother being on the IPv6 Internet when you're already fully accessible on the IPv4 Internet.
And behind several NATs which apparently is good because a single IPV4 address can belong to millions of people so you can 'blend in', as it were, if you enjoy privacy.
There are already resources you can't get to with IPv4.
Also IPv6 is being mandated by the gov't (https://www.whitehouse.gov/wp-content/uploads/2020/11/M-21-0...). You might be able to ignore it and retire before it's the 'default', but deep knowledge of IPv6 is rising in demand.