The Rural Purge mystery

In 1969 or 1970 or so, CBS instituted what was later described as the Rural Purge. Highly rated shows like "Green Acres," "Petticoat Junction," "Beverly Hillbillies," and "Mayberry RFD" were all cancelled. They had high numbers, but they had the wrong numbers. The Nielsen people started studying the demographics of their audiences. Advertisers no longer wanted big numbers, they wanted urban viewers, urban viewers with disposable income.

The rural shows were replaced with "Mary Tyler Moore," "Bob Newhart," "Arnie," "All in the Family," all shows that took place in big cities.

The experiment was a big success, it seemed counter-intuitive to cancel high-rated shows. But the advertisers were happy.

(Tragically, if they had gone by demographics only a couple years sooner, they would have never cancelled "Star Trek." On the plus side, demographics were the only thing that kept "Hill Street Blues" on the air.)

Here's what I don't understand, why would CBS pick up "The Dukes of Hazzard," the very definition of a rural show, only 7 years later?