Can CU afford to put the students sidelines? Wasn't that one of the reasons they were put where they are? So the sideline seats can be sold at a higher price than what the students pay?
One of the many reasons.
The biggest issues is logistics. Either CU must block out 5 rows of seats behind the students so that people sitting can see above the standing students, or they must rebuild the entire bowl to put a wall behind the students in order to raise the first row of seats up above them.
Basically its a huge pain to put them there if the stadium wasn't built for it.