The problem is that you seem to not consider what put him at an other level, it was his consistency not the level of his peak. Also it's worth keeping in mind that there was only 9 player of month given, Ronaldo wasn't the best performer during the first three months and barely played during the first month. He then won 2 out of six awards when he got into rhythm and Torres won 1, the other winners were Agbonlahor in November when Ronaldo played less games, Santa Cruz and then Ashley Young who was more productive in April.
Now if you want to look into it, there is only one month that he could have won but didn't, it's December where he scored 7 goals and provided 2 assists while Santa Cruz scored 6 goals and provided 1 assist but maybe Santa Cruz was indvidually better during some of these games.