Then explain why film-makers never bother to add any Batfam member to Batman's movies? If these Bat-fam members have such large fan base, shouldnt Batman movie feature them? But instead film-makers think its not worth the money to cast actors for the roles of Batfam members.
If there is anything, you see they are not that valuable when Harley makes it into the Batfam due to how profitable of a character she is more than most other Batfam members.