The committees exist essentially as an antitrust defense - "Look, see, people outside Google have an influence on this project!" - we'll see how effective that is. As to why someone would sit on such a committee, that's a much better question. I suppose they might be flattered to be invited. It looks good on a resume and they might get some speaking gigs out of it? But I don't see how someone with the necessary expertise to be considered could also be ignorant enough to take Google at their word.