"Datacard" is a type, and there are no subtypes to it for automatic categorization, unlike Ship and CR-90 or Item and Vibroblade. As I believe both TFM and Centrepoint would use the Web API as much as possible, I think the reason is 'human nature' aka path of least resistance. They'd have to set up sub-categories for posters to choose in order to properly select the entity.
So like... DC -> Select Entity Type -> Select SubType
As for the TF market we also have the Datacards listed under each factions individual shop. Reasoning being each faction leader manages their own DC assignments and we are running between 3 or more people for Das to be assigned.