Also, high ratings don't necessarily mean that a network thinks a show is doing a good enough job. To give you an example, in the late 1960s, CBS dominated the Nielsen ratings, its shows consistently coming in at number one. So why did it retool its lineup in the fall of 1970? Because the people who were watching were over 40 and not that magic 18-? demographic that they feel has the disposable income to spend on the products their sponsors advertise. So a lot of high-rated shows went by the wayside because CBS felt it was reaching the wrong people. While Enterprise never was a ratings giant, it could be argued that UPN felt that it was drawing the wrong audience.
With the casualties of CBS' mass cancellation including Green Acres, Petticoat Junction, and The Beverly Hillbillies, along with Gilligan's Island and The Wild Wild West going a few years earlier and Gunsmoke going a few years later, the running joke back in the day was that CBS cancelled everything that had a tree in it.