Well, there was syndicated drama before TNG. Things like Highway Patrol, Sea Hunt, and even The Adventures of Superman were first run syndicated shows. Even shows like The Avengers, Thunderbirds, UFO, and Space 1999 got syndicated in the US from overseas. But during the 1970s, syndicated shows slowed down because stations found it was cheaper to run reruns of Gunsmoke, Bonanza, Star Trek, Gilligan's Island, The Brady Bunch, and I Love Lucy (in "strip syndication"). By the mid 1980s, syndicated shows were basically dead though so you are correct that syndicating TNG was a big risk. But it was really their only option after the fledgling Fox Network passed on airing TNG.