The advantage of the AppleTV is that it's basic consumer hardware that a lot of people have, that you can provide for them at a reasonably low cost if they don't, and that doesn't really require much in the way of tech skill for the person whose house it's in to keep it up to date. You don't even have to do anything to update versions - tvOS will do it automatically.

I can't find it right now but there was a post announcing the port to tvOS on their blog where a developer from the UK (but living in the US) talked about how it let him buy, configure, and ship a simple consumer box that uses little power and needs minimal hands-on maintenance to his parents' house as a replacement for a server he had been running in their house as a VPN endpoint for this sort of thing - so he could watch BBC, etc.

I wouldn't want to update a RPi that's in someone else's house on the other side of the ocean.