Why can I own 17 apple devices but only be able to share movies I bought with 10 of those devices?

I want movies/TVshows , etc. that I buy to be available to all Family Sharing member devices. Unfortunately in order to do this all members must have "Media and Purchases" logged into the same account, even though each member is logged into their devices with their own AppleIDs. Even more unfortunate is that the shared account can only have 10 devices associated to it - so if all 5 Family members have an iPhone and Mac each the 10 device slots are used. Suddenly someone in the family buys an iPad but they can't view the movies/TVshows because the new device doesn't get a shared account device slot! This is frustrating of course.

Why does Apple's model not allow at least 1 device of each type (iPhone, Mac, iPad) for each family member view the movie/TVshow content? By my math increasing the limit to at least 15 makes more sense than the current model. I would even be willing to pay extra for the service.