(1) On a practical level, although I don't know Greg's personal financial situation, he was the CTO of Stripe for five years. He's rich enough not to work. He works exactly because he's enthusiastic.
(2) Secondly, to say that Greg merely handles logistics for OpenAI is to willfully ignore the post as written, and the reality on the ground.
Also, I'm not sure Sam is a billionaire, although well on his way.
It would have been fine if he was just telling a story about his own life, but when he said "make sure you also have someone like Greg" it became fair to point out that he seems a little bit oblivious as to context.