I made a post about this subject on another thread not that long ago.
Many women would rather date a guy that was less attractive as her if she is a bit insecure or fears being cheated on. Let's face it, the average man in America is not particularly attractive at all, as a significant portion are overweight and out of shape.
Now, let's say you have a cute but normal girl, say a 6 or 7, and she is approached by a 6"3", broad shouldered and ruggedly handsome man. She might be attracted to him but she is also aware that many other women will be as well, and without knowing much about him she risks being pumped and dumped, cheated on, etc. If she had been hurt in the past she'd be even more likely to disqualify him over the tiniest of things out of insecurity.
I'm 6'4", white, broad shouldered and in really good shape and I get rejected A LOT. I've been to speed dating events with 5s and below and didn't get a single match, no responses on OLD, etc. I'm not saying I belong on Vogue magazine but there is definitely some truth to all of this.