Girls got excited while riding stallions, so it's not surprising that when they saw those guys they jumped on them. Well, their chosen pose is exactly what I pointed out in the previous sentence. It has always been a mystery why so many girls love horses, actually this video partially answers this question.
That's what I call a bundle of money, apparently pumped up guy really was tight in terms of sex. The brunette did a good job, she relieved the dude's tension.