Because content providers are making you care about that. They _demand_ that you're prevented from seeing high quality TV if your platform doesn't fully lock you out.

Do netflix limit their own shows?

Yes, they apply full DRM to their own content as well.

The answer is probably "because your content is locked on that provider", but that's a less and less valuable point.

Obviously, BitTorrent was the big reason in the past, but now the reality is that there is a lot of competition in the video space - you aren't just competing with films and tv shows, but youtube videos, twitch streams, etc...