It's purely a consumer mentality, the same way someone would shop at M&S, Waitrose etc over Tesco or Sainsbury's. It's the label, the illusion of quality. Although of course, sometimes quality will be there, sometimes not.
Same with the escorts themselves. They see themselves as a brand, and the high-maintenance ones (that's a polite way of putting it) apply the same logic to themselves. "I'm not a Greggs pasty, I'm an M&S baked pastry"
I can understand why some escorts who are both objectively gorgeous, great in bed, genuinely enjoy themselves and go out of there way to provide a great experience (location, clothes, etc not just services) can justify their cost, but only so much. Beyond £150 is taking the piss.
On top of that, there's the mentality that the guys with money to blow on £200+ punts aren't going to be "common" or dodgy, or unclean or whatever, so escorts in some areas naturally charge more just to avoid the "great unwashed".