How about this then? There are members from Microsoft, Twitter, and Pinterest on the project's technical steering committee: https://github.com/ampproject/meta-tsc
This is not new information, it just brings us back to where the conversation started. I'm not pointing out that there wasn't an open standards body or that big name corporations were not part of it I'm pointing out none of these had/have a vested interest and bigger control of the implementation beyond how it is consumed.
You don't think engineers at major companies using the standard have a vested interest in how it is designed? Even considering that those engineers are on a committee whose entire purpose is to influence the design of the developing standard?
Individual engineers may or may not, those companies however stand to make no change in margin by agreeing or disagreeing with Google on how the AMP works behind the scenes.