He was not a dummy who would simply spam Forestep to its absolute maximum in every single fight. In this case, he had already figured out that there was little point in trying to fight a symmetrical battle against Kane centered around maneuvering. The fact that Kane had more maneuvering techniques, a Martial body whose spec configuration was centered around motion, and the original and superior version of the Forestep technique meant that he was most certainly going to dominate Rui in a maneuvering battle where they both capitalized on speed and agility.
Thus, Rui ruled out such a battle. This was the kind of logic that he had included in the VOID algorithm when he created it, however, he himself didn't need to follow the protocols of the VOID algorithm that were meant to dumb down the process for fighters. He could produce a better result with his own critical thinking.