I know the show was on a long time. It didn't have low ratings did it?

By the 1971-72 season, its 12th and final season, it had dropped out of the Top 30. In the final season, it was moved around on CBS' prime-time schedule which adversely affected viewership. CBS did the same thing with Murder She Wrote in 1996. After 12 years on the air, it was still doing good, but they moved it opposite Friends on Thursday nights and the Murder died a rather quick and unceremonious death. Plus, by 1972, CBS was trying to improve its image and preferred shows like The Mary Tyler Moore Show and All in the Family rather than leftovers from the 1960s like My Three Sons.