I don't think it was the selection of rentals, but other reasons including: Apple TV wasn't as popular as it is now [1]; and, most likely, you're already paying for TV Service with your internet service provider - so why you would pay (again) for a show you've already paid for? (And, most likely, you're paying for DVR service, so you could have just recorded your show for future (and, potentially, unlimited) viewing.)

1. http://daringfireball.net/linked/2012/07/24/apple-tv-xbox