Also sprinting on the track requires maximum effort. Meaning trying to get as much as your legs/core can produce. On the road, all of the sprints are sub-maximal. The sprint at the end of a crit (even a short one) isn't the max that your body is capable of producing. It's the max that your very fatigued body is capable of producing.
Compare a 1-rep max squat when fully rested to a 1-rep max squat after running a 5k.