This rule was put in place long before my reign, but I think I can shed some light on this for you peasants.
The thought process as to why assists are worth less than goals is that it is easier to get an assist than get a goal (you can be one of the two previous people to possess the puck vs only 1 goal scorer, plus every goal always has an assist).
As to why goals are worth the same as points, I have no idea. You would think it would be something like goals/10, assists/12, and points /15 or something like that.