Apple TV was once called a hobby and it still feels that way to this day. A move initially to allow Apple the space to figure out what they want it to be, that vibe has gone on for so long, I think consumers and the media industry sense it too. They have been unable to persuade the media industry to embrace Apple TV in the same way they did with the music industry and iTunes.
Their own programming is a good defensive move, make content to fallback on if current deals fall through and if the shows are popular, Apple can leverage that in future deals. It may have to offset the eventual saturation of the devices markets, you can only sell so many Mac and iPhones every year.
People – perhaps rightly, considering the hobby status – seem to question Apple making their own shows as if they should stick to what they know, but we have been proven wrong by Netflix and Amazon already.