It's the early 70s.  Gene Roddenberry hit it big with Star Trek and is looking to create the next big thing.  He pitches Genesis II to CBS in 1973, who is not interested.  He tinkers with the format a bit, pitches it to ABC as Planet Earth in 1974, and is shut out again.  There was a third pilot with this format pitched a year later and guess what?  Three strikes and you're out.