The about page at http://schema.org/docs/about.html states that the steering group "includes representatives of the sponsor companies, a representative of the W3C and a small number of individuals who have contributed substantially to Schema.org" which would seem to amount to quite a few people.

Yet, "The People" section only lists 5 steering group members, 3 of which are from Google, nobody from the other sponsor companies and W3C, as being part of the steering group.