Which is essentially intervals or Fartlek, which is again how middle distance runners train. Strictly speaking, the rules don't force that, nor do they force the length of the "sprints", the opponent does. Plus a there is a rule of thumb in wrestling (not sure how well it applies to other combat sports) that reacting takes twice as much energy as acting; so if fighter A can keep fighter B on his heels the whole time, fighter B will break first, even if their conditioning is equal.
Besides, without good conditioning, one will never be able to handle the same volume of skill specific training, which in turn means ones technique will lag behind its potential.