One thing to consider is that a lot of men aren't very familiar with make-up. They might say that they prefer women without make-up, but not realize that many of these girls ARE wearing make-up (either a small amount, or even a lot...but she's really good at doing a "natural look").
I also think that one thing that some guys worry about is that they'll start dating a girl who looks really pretty with make-up, but when they get to the stage where they see her without make-up, she doesn't look nearly as good as they thought she did. So, really, what they want is a girl who looks really good without make-up, but a lot of women wouldn't meet their expectations without make-up.
Guys prefer girls whose makeup appears as if they aren't wearing any