You have to figure your chances of converting against CSU are better than they'd be against Southern cal, for instance. Lots of things factor into the decision to go for it on 4th down. Distance, your confidence in your kicker, your confidence in your punter, your confidence in your offense, confidence in defense, game clock...
Sure. But don't you think the defense would play better with a field position advantage? Getting just around the 50 can be a successful drive for the offense.