That's very interesting. I had always thought of role model as referring to a specific individual, I haven't encountered the idea of collective role models forming "cognitively available success cases" before.
Well for example, why would a boy ever believe he is even capable of certain career paths if he's only ever seen females in those roles? When there is little representation, the idea becomes that only that demographic is capable of the career. An example can be seen in esports like Starcraft. When the Koreans began to dominate the competitive Starcraft field, other nationalities began to cease even believing they were capable of equal success. A similar view has been common with, say, black people and track+field sports like sprinting in the Olympics.