it’s kind of defensive. Right now Apple doesn’t have a tv service so Apple customers rely on third party parties.
that means that Netflix, Disney, amazon etc.. have a hold over Apple in some way. If Netflix or HBO or some other company decides they want to withhold there service from Apple devices for whatever reason that’s going to effect sales of Apple devices.
Apple can’t battle these services in terms of content, they are too big. What they can do is a) produce their own exclusive content so they have some bargaining chips. If they have some popular shows that the public like it provides bargaining power with studios who might not want to offer there content on Apple devices.
b) if Disney or Amazon ever decides to withold tv services from Apple their customers have at least something to use that is reasonable.
c) in the long run owning some tv shows can be big business (game of thrones, friends etc..)
ultimately Apple don’t like relying on third parties for anything. Look at their plays over the years. It doesn’t even matter if they don’t make much money sometimes. As long as their customers have access to all computing functions at some level that allows them to sell phones with exclusive operating systems that don’t have a lot of market share.