The first things filmed EVER were reality based. Plots didn't come until later, after people got over the initial shock of the technology.

The people in "An American Family" were actually from Eugene, but shifted down to L.A. at some point in their story. Since most people in town knew them, we couldn't appreciate the show much, as we knew the difference between their real characters and the pretenses they put on for T.V. There was not much reality, but there isn't likely much in other such shows, either.
Things quickly became dicey for anyone else whose name was "Lance".

In the 50s and early 60s, Edward R. Murrow had a show where he visited celebrities in their homes and got down very cosy and casual with them. Just because they weren't addicts, criminals and weirdos, didn't make it any less a reality show. The subjects soon forgot about the camera and acted like their natural selves. The show with Louie Armstrong was my favorite.