Your objection is funny. Other methods of communication could be faked. Here you have Github as an authority to check membership and the organisation's repositories as an official place of discussion (perhaps equivalent to the website).
You do have to trust that the org is legitimate, but you could also fake a website or a whole organisaion.
The GitHub org member list is not going to be an authoritative list of all delegates from all members that all have GH accounts. One of our W3C participants conveyed our objection and he isn't in the GH w3c org member list.
I mean, I see what you mean, but to a casual observer that's not very clear.