I understand that this seems arbitrary, but look at it from this perspective:
Starbond values are supposed to represent the average gross of the star's movies.
HSX determines what movies go into a star's TAG using objective criteria - a credit in the movie's main credits/publicity materials. This is easy to verify, easy for traders to verify and can be done without going to see every movie that has a moviestock.
The producers decide whether to include an actor in the main credits (or not). They're not thinking about HSX when they do this. They're thinking about publicity, their working relationship with the actor, etc.
This can lead to outcomes on HSX that seem arbitrary, like GSHAN. But the arbitrariness comes from producers deciding which names to credit, which we have no control over. So, accept it and move on.