American TV shows were more popular than Chinese shows so the government had them removed to allows Chinese shows, unimpeded by foreign competition, to flourish.
Here’s a Chinese article describing this and a Chinasmack post with commentary.
At least they still don’t care about copyright law and you’re free to download whatever you want, or buy pirate DVD’s or Blu-Ray. But you can’t stream them because they’ve been harmonized.
edit: beat me to it Ben. I agree with your point about downloading being preferable anyway. Chinese video streaming sites are low quality and heavy-handed with advertisements.