Vast Progressive Conspiracy?

It just struck me. Hugh Laurie as House. Kevin McKidd as Owen Hunt. Andrew Lincoln as Rick Grimes. Daniel Craig as Jake Lonergan. Charlie Hunnan as Jackson Teller. I have no problem with non-Americans in TV and Films made in America, but I've noticed there is a trend for British actors to play Americans. It's great to see them conquer the American accent, But I wonder why it is suddenly so prevalent. There are many, many fine Americans trying to get that defining part. I'm really okay with the diversity of characters as witnessed in the original Star Trek series of the 60s. But they had an oriental play an oriental and a Russian play a Russian. As the series was recreated, this was done many times. But here we are talking about main characters in a series who are Americans played by non-Americans. We're not even talking about someone like Steven Yeun playing an Asian-American which he is, but a Foreign national playing a native born American and not a supporting role. This sounds bad, I know, and the actors I've mentioned are great at their job. It's just a trend I started to notice and wonder if there is an agenda behind it, or what it really is. What really pointed it out to me, was watching Sons of Anarchy, where the bikers are in Ireland and the actors are surrounded by Irish and British accents, and Hunnan's accent starts to slip. I don't know anything here, and I'm not trying to stir things up, I just noticed it and wondered.