I cant imagine there is a better place to be an escort than in Las Vegas.

More hotel rooms than any other state, and all so close together.
More conventions than any other state.
And more visitors/tourists per year than any other state, with loads from the UK and other European countries.

Oh to be an escort in Fabulous Las Vegas ()

From the reasons that you stated, I would say high demand makes it the top city for providers. I am not sure about the supply though. If there's too much supply then it will make it less desirable.