Galactica

The original Galactica was in my opinion, good, but the reason why it only lasted one season in my opinion are as follows:

-The effects did not look original, so it was seen as a Star Wars Ripoff.

-It was seen mostly as something for kids at the time, so adults felt no use in watching it.

-The sociopolitical sitcoms of the time(All in The Family, Sanford and Son, The Jeffesrsons, etc)were winding down and prime-time soap-operas like Dallas and Knots Landing were starting to get big, so it was doomed from the beginning since most people at the time would rather watch a prime-time version of daytime drama like Dallas than a sci-fi epic series on television. Dallas debuted at the same time period as Galactica.

-No such thing as "first-run syndication" existed at the time. It probably would have gone on longer if it had. I don't think frist-run syndication existed until Star Trek: The Next Generation came on the air in thae late 1980s.