It's basic advertising sense — given that new customers only have their photos (and reviews... But who gives a negative review these days) to base "purchasing decisions" on. So those who advertise better charge more. Those who are also younger, I think tend to charge more.
In my experience, I've met with service providers who aren't super high on the looks department but whom, within minutes then, I thought "man, this guy probably has many skills to offer" and usually that's the case and they don't disappoint - the give oral better, etc. I guess it's sort of "evolutionary" in their industry: they have to find their special edge/ niche.
For some, it's just being hot and taking good photos.