UNC got away with it because they went big. Sounds crazy but is true. The fake classes were open to all students, not just athletes. Athletes were pushed into/encouraged to take them, but the academic fraud wasn't limited to athletes. It was actually more of a threat to their SACS accreditation than any NCAA trouble. That might have even part of the calculation on their part. Create the joke classes for the athletes to take and keep them eligible, but not necessarily cheat on behalf of anyone specific by letting anyone take them.
What Mizzou did was centered around athletes - this tutor completed work/cheated for specific athletes.
NOW we know why the Duke student body used to chant, "JR can't read!!"