Guys usually find the same physical features attractive, unlike females who have a more detailed criteria. For instance:
A might think Trey Songz looks like a pigeon.
B might think Trey Songz looks like a rock-my-socks-off kind-of-lad.
Because all guys usually find the same girls attractive (there are anomalies), the same girls get approached and girls who get approached learn how to reject people. Guys who get instantly walled off or rejected don't try further.
And that's why most popular and hot girls seem to have the personality of a rock. Because a lot of guys don't persevere - and whoever does persevere, I hope you do it in a PC way, not in a way worthy of a newspaper headline - they never find out what the girl is really like.
Just my two cents. In other words you just need to dig a little deeper, and shrug off that 'first defense', because popular and good looking girls have had guys try to flirt with them so many times that they probably group guys who approach them under one category. Time-wasters or hedonists with a seemingly gargantuan ego that pops as soon as they get walled-off.
If you want a girl, then prove it to her. If you fall over at the first hurdle, you're not worth their time.