CBS got rid of all of its hit rural-themed shows (Beverly Hillbillies, Hee Haw et al) for the same reason, plus they wanted to change their image to a more sophisticated image. So, out with Jed Clampett and Aunt Bee, in with Archie Bunker and Mary Richards, or as Green Acres' Pat Buttram famously said, "They cancelled everything with a tree in it".
This part of the story I'm already familiar with, and respectfully, am I glad they did this.... We got a whole new slate of some of the smartest and funniest shows ever, and said goodbye to all those rural shows, most of which might have been seen as insulting by Southern and rural viewers. Mayberry RFD was respectful to the South, but not many others.
This is exactly the moment in TV I think of, when contemplating how horrible things are on broadcast TV now. They took a huge risk and it worked. Turning things around now would require just that kind of decision.