Because her ass is very small.... like I said, that doesn't make it bad, it just makes it small. That image actually works against your cause since the hourglass shape refers to a woman's body shape when looking directly at her, from the front (or back I guess but the arms would make that look different since they are further back that the chest) while she is standing straight up.
Also, the power in your thighs comes from your quads (which are in the front of your legs) so "powerful thighs" is probably not a good descriptor for her legs in this instance. C'mon man, I though you were the authority on the human body. You can't go around, getting all aghast when people question you, then miss something as basic as this.