I've been with a couple of providers who just love to have sex. These folks got wet quick, would go forever, and really didn't want things to end.
Others were a good time, kind of had a scripted session, I enjoyed myself, but you could tell that if the $$ weren't there they wouldn't be either.
Double winners are truly a treat.
I like it. Although I am not sure about the wording of your premise. It seems to imply that these ladies are nymphomaniacs. From the rest of the post you show that you mean that these ladies enjoy sex and bring that attitude to their job.
May need a rewrite, although I can't think of a better way of rewording it.
I know I have paid money for women that had I met in a bar, I would even THINK about taking home.
Rocket
you assume that because a provider enjoys sex, she will enjoy sex with clients which can be an entirely different proposition.
Remember the discussion regarding whether providers have orgasms with clients? Not so encouraging. There were also a number of hobbyists who didn't appear to care whether the provider enjoyed herself or not.
I love what I do as a profession, I couldn't do it as a hobby (need a license) but I don't think I would do all parts of it for free.
One thing I've learned about evolutionary biology is to beware of glib analogies. I first learned it from reading essays by, you guessed it, Stephen J. Gould. Evolutionary "success" depends on producing more surviving offspring than "rivals" (if this doesn't get too long I'll explain the quotation marks later). Doesn't have much to do with this topic, does it?
OK, we can still play with evolution as a METAPHOR for things that go on in the hobby. On that level, there's no paradox. Women who are more suited by temperament, libido, or whatever to being providers are more successful at it. Nothing paradoxical about that.
Ah, but wait, things are a bit more complicated than you make them. Accident, self-fulfilling prophecy, and feedback loops all have a role here. I'll use moderately large numbers because it's the statistics that matter.
Let's imagine 200 women just starting out as providers. Better to think of them as geographically scattered than as 2 platoons facing off. Half of them, for whatever reason, get a good trade with nice clients right off the mark. The other half, also for no identifiable reason, have slow business and some real jerks showing up. I think it's obvious which group, ON AVERAGE, will feel better about being in this business. This could start feedback loops (one positive, one negative) whose result is your premise, i.e. your starting point.
Of course in real life both mechanisms operate and influence each other, along with many more. The point is that simple "common sense" analysis rarely works with complex systems.
Sorry about the length.
this is the right way to look at it (even with no geographic isolation, a la the "Galapagos Islands" 
it's called the science of "Complex Systems" where feedback and local interaction are key
see http://www.complex-systems.com
This is just an opinion, of course. I have to believe all escorts who make it past the first few months enjoy sex to a high degree. Its a matter of with whom...some with lots of different men, some with very few. YMMV is so true. The financial success also comes from good marketing, screening, and attitude in order to develop a strong list of regulars or repeat clients, and those are the ones where there is "chemistry". Here, its not just work. Clients don't return unless they too feel that connection through great sex, great companionship, etc. Otherwise, its a one-time deal where the more convincing the "acting", the better the resulting review. This I see as real work. The goal here is money and advertising, which leads to more potential regular clients. The only paradox I see is...if an escort is too good an actress, she will have too many returning clients with whom she doesn't enjoy sex with. Less enjoyment I imagine can make it difficult to get out of bed every day, or should I say into bed. Of course, her clients will eventually see that the "relationship" isn't real.
Thus, financial success comes from not only the ability to please clients because one enjoys sex but also the ability to understand how to maintain a steady flow of income by carefully selecting clients who can develop into regulars. In short, women who use both their head and their heat are the most financially successful. As far as evolution goes, sexual enjoyment will take one to the next level but develop of the cerebral cortex is what is needed to continue further up the evolutionary tree. Now, what about survival of the fittest.
I think the real paradox here is one of roles: who is the provider and who is the hobbyist? The most interesting encounters I have had left me wondering.
The Third Man
Let's suppose that those who are paid the most "sacrifice" the least, that is, in economic terms it costs them the least to provide.
By analogy, suppose you are able to produce very good widgets for $50 each, and you've found the market will pay $75 apiece. I, however, being very clever, am able to produce excellent widgets -- demonstrably better than yours -- for $25. The market will pay me $100 for my widgets (we're ignoring elasticities of demand here -- let's suppose the market will bear those prices for all the widgets you and I can make).
So your widgets generate producer surplus of $25, and mine generate producer surplus of $75. The $75 is mine, and the fact that your costs are higher is your problem.
The happy provider should get paid market for what she provides. What it costs her just factors in her decision whether, and how much, to provide.
