I think they're extremely scared about their Enterprise github.com customers being unhappy when their IP allowlists or IP address audits are impacted by a switch to allowing v6 addresses, as this will surely lead to tons of headaches for their account managers.

To add, if they're moving to Azure this might make IPv6 deployment complicated: https://news.ycombinator.com/item?id=29327773

Github also can't send webhooks to ipv6 only hosts.

Did you make a pull request?