Serious question here: are most native Coloradans not big football fans?
Here's my less than scientific observations and suggestions.
Excluding CU alum, the inhabitants of the front range generally dislike Boulder, or perhaps see no point in going there. From the moment US36 backs up at the Colorado Ave traffic signal, Boulder is a hastle. Parking down town is tough. Real Estate is out of reach. The town is elitist and doesn't appeal to Joe six-pack. Why go to Boulder if the welcome wagon is snooty? You can get better shopping in Cherry Creek, Downtown Denver, and at any number of fancy malls and shopping complexes. The Boulder infrastructure doesn't handle big crowds well. Whether it's the Bolder Boulder or a football game, you are guaranteed to be backed up in traffic somewhere in town and you will be not happy with the parking situation.
Fix: Make the Boulder turnpike 3 lanes in each direction and have it flow through town with no traffic signals. Build overpasses or dig a canyon for traffic to flow all the way through town. Create ample off ramps and long frontage roads along the side of 36 and big two lane exits for Baseline, Colorado, down town (Arapaho, Canyon, Pearl) Valmont, Iris, and Jay. Double the parking downtown with more multi-level garages. Boulder could use a few really nice large resort hotels, too. The hotels in Boulder are either over priced, and many aren't exactly keeping up with the times. (Pools, fitness rooms, conference facilities)
Issue 2: Diploma dilution. The Denver area has a large higher edutainment infrastructure, with gobs of institutions offering diplomas. Metro, Red Rocks CC, CSU-Denver, CU-Denver, DU, Regis, Mines, Arapaho CC, DeVry, U of Phoenix, Johnson & Wales and others have crowded out the marketplace. Alumni from these schools, plus from outside of Denver (Ft. Lewis, Western State, Mesa, AFA, Colo College, Northern Colorado, CSU-Pueblo, Adams State, Colo Mtn College), or graduates from any number of out of state schools makes it difficult for CU to connect with vast numbers of college educated Coloradoans. Lots of these schools don't have football programs, or if they do, there is not enough intersquad interactions with CU to create interest or rivalries.
Fix: Colo's higher ed market is ripe for consolidation. Do more to get highschool and college kids in Denver indoctrinated into college football culture. It might help if DU had a football program, or if CSU played more games in Denver to help stimulate interest in CFB. If CU had the option to play more teams located in the Denver area, it would certainly raise the profile of CU in-state.
As it stands, the Broncos and the high priced NFL tickets are a more than adequate substitute for the college game in elitist Boulder.
Boulder USA is more accurate than Boulder, CO. With 45% of students coming in from out of state, and with the football roster lopsided by out of state players, there are few home town heros on the field, connecting with the area's high schools. This dynamic further distances the emotional bond between Denver's vast metro area and CU.
Fix: Convence OOS alum to buy season tickets and have a program where those tickets get in the hands of as many Colorado youth league players, highschool students and teachers as possible.