Because like OU and OSU, they wanted to have on the front page of their mission statement that they only buy green power generated by wind.Why would anyone in their right mind choose to pay more per Kwh for "wind" when the lines that come into your home are not even connected to the "wind"?
Yes, we all know that's a minority of the power flowing in the grid, but they buy enough towers to supply what the colleges need to operate on. It's all about showing ones dedication to "saving the planet".