for the same reason women want "responsible, caring, real men" and then hook up with jerks.
Simple answer because you can't always get what you want. Me personally I don't like females or will date a female who puts so much makeup on their face. but i still think some celebrities (Nicki Minaj) who is all fake is good looking but i wouldnt date them.
The media shows guys a false example of "natural" girls so they THINK that's what they want and are surprised when girls aren't realistically like that. The internet and magazines photoshop girls so that their skin and body size are unattainably perfect while acting like this is just what girls look like. I once googled girls without makeup, natural beauty, etc and it showed me pictures of girls that were OBVIOUSLY both wearing lots of (natural looking) makeup and also their skin was clearly photoshopped (I mean nobody looks like that in real life). In magazines they photoshop girls to be unrealistically skinny so guys see actually skinny girls as average, and average weight girls as fat. When guys say they want a girl with natural beauty, they are usually thinking of the "natural beauty" of the photoshopped perfect girls on advertisements
Same as why girls claim that they want good guys who would treat them right but the truth is they're into hot bad boys
Because they are immature
Because nobody would want to admit that they are shallow.