Why would I pay for this?

Why would you pay for any streaming service? To see their specific content.

The subscription is for Apple TV+ (note the distinguishing ‘plus’), a streaming service with Apple-produced content. Subscribing to this service is the way to see these ‘Apple Originals’, as they are called. You can see the current shows on this page or this page, or differently organized (including upcoming) at the Wiki.

A lot of subscribers will have gotten a free year worth with a hardware purchase. I wonder if Apple will share those statistics in an upcoming event.