JoshJames, your female platies are not all females. The young ones that all look like females have just not developed their typical sex characteristics yet. As they begin to reach a mature size, some of them will turn out to be males. The lack of obvious males in livebearers is normal in platies, swords, endlers, guppies and mollies. In swords it is so extreme that lots of people will tell you they change gender and are fertile afterwards.
I have 5 swords that I got when they were very young. All look like females right now although they are about 2 1/2 inches long. As they mature, there is one that I am fairly sure will turn out to be a male but at a glance he looks like a female from the shape of his anal fin and the fact that he has no sword. He is only about 4 or 5 months old and just needs a little more time to mature, but I can already see the beginning of a slightly thicker bottom ray on his tail and a slightly heavier leading edge to his anal fin. A month from now most people will be able to easily see that he is a male but today it still takes some studying and I can't be certain.