Ratings are nice but they don't count. It is ad time sales that count. If you have less viewers but sell the ad time for more, you make more money, and that is all that matters.
Ratings have never been accurate anyway, as Nielsen isn't scientific. It doesn't tell you what people are watching it tells you what NIELSEN families are watching.
UPN did well in some markets like Atlanta and Chicago. In fact WWME Low Power Channel 23 does very well in Chicago by appealing to black viewers. Since blacks tend to live in the city proper and can get the low power signal.
I don't know maybe the CW isn't selling well, but it really hasn't been about ratings for years. I do miss Reba