All the techniques in Karate were created for killing the opponent with only one blow.
This is called "Ichi-geki Hissatsu", the same meaning as "Ippon".
Thinking of this, ni-hon (2 blows) or san-bon (3 blows) does not make sense. The player was killed twice or three times? They should be changed to ni-ten (2 points) or san-ten (3 points)..
Anyway this is the WKF rule. But at least karate-ka should know the genuine meaning, don't you think so?