it doesn't matter if it works, it still leaves the groin and leg open to attack. The mechanics and realities will still be the same. Kick too high and you'll expose your standing leg. Here I'm sweeping the leg, but I could have easily done a low spinning back kick or high sweep to his knee. Had I been facing forward, I could done a front kick the standing knee or thigh or grown, Had I been in a side stance I could have done a low side kick to the thigh, knee or shin of the standing leg. If MMA fighters don't know how to exploit the high kick then you won't see them exploiting the high kick.