The other possible reason is that HSX hasn't gotten around to it yet.
HSX will attach a starbond to a moviestock when the relevant actor (or director) has a credited role in the movie. Not every appearance in a movie is a credited role.
For HSX, a credited role means the actor is:
- listed in the main credits for the movie, or
- credited on publicity for the movie, such as trailers and posters, or
- credited in the production notes for the movie.
HSX will also attach a starbond to a moviestock when there is news that the relevant actor will appear in the movie, or is in talks/negotiations to do so. This is done in anticipation that the role will be credited.
Starbonds will not be attached to moviestocks for:
- uncredited cameos in the movie, or
- cameos listed only in the closing credits of the movie (and not in the main credits), or
- actors being listed as part of the cast on IMDb's page for the movie.
Whether or not a starbond should be attached to a moviestock often becomes clearer in the weeks before a movie's release, and HSX may defer attaching some starbonds until after they have confirmed acting credits in the production notes for the movie.
If you do come across news or publicity that suggests a starbond should be attached to a moviestock, you can post your suggestion with a link to the evidence on the HSX Forums, on either the Stars board or the Feedback and Support board.