Sounds like a dumb question on the surface, but maybe it's for the same reason that more women aren't brain surgeons. Maybe only a few can qualify.

Using pure logic (flexible hours, relatively high hourly revenue, very enjoyable activity), it would seem that only a few would NOT be providers, but clearly that's not the case.

Probably the main reason is the social and legal environment, but in places where it's legal, there are still fewer than logic would suggest.

Men don't make passes
At girls with glasses
...except those with very nice asses

Most women do, only within the confines of marriage which is a kind of legalized prostition; people will never admit it to themselves, yet when push comes to shove in divorce court, that's about what it comes to.

......that is set up. Once a provider or client crosses that barrier there's a chance it could mess up the provider/client relationship. Some women get through the business by thinking of men as walking ATM's. This is especially true of the younger providers i.e women in their 20's. I prefer to see mature providers in their 30's and 40's.

Sir, you state as one of your positives about being a provider is "enjoyable activity" If more women held that opinion there would be fewer men in need of providers. Please keep in mind that there is still a large portion of our population still floundering in it's puritanical beginnings and believe that sex is for procreation only and to do otherwise mocks God. That is why we see so many beautiful women who are as cold as lake Erie in February. It sucks but I believe that many women are still brought up to think that sex is nasty not to mention any of the extras that we have grown to call sex, specifically, Oral , Anal, Russian etc..... Thank God some women have risen above the BS and do have fun with it.

I am convinced that being a provider is not all that easy...  while there are some gents out there who do this truly as a hobby, there are those who are less capable of attracting and holding a legitimate, intimate male-female relationship.  These too, visit our female friends... and the result - well - we have all seen the complaints - bad breath, limited social skills, brillo pad body hair... BO, etc.  I would suspect that these individuals are a reasonalbe portion of the Bread & Butter of the biz, while the "diamond Jim Brady's" run in to the single digit percentage points....  This eliminates many women who cannot (mentally) be with a man she does not even like, let alone love....

Then there is the 'even if they were providers - who would care' factor...  Ever go to the gym?  I go to one where there are no studs - but there are no femme fatales either.  Walk down the street - how many truly attractive females do you see - in "Reasonable" shape?  

Finally - being a provider -when you take the costs out - is not that good a business - yes, you can make money.... but! and here is a big but.... you provide your own health care, place of business, phone and com costs....ad costs...etc.  and like an athlete - you have a limited amount of time to make the maximum income.... so ya better be stashing it away.

yea - the grass always appears greener 'over there'   Not a dumb question... because I wonder why so many are in - who are really good looking....  

"Very enjoyable activity?"  Perhaps to you.  I daresay that to many women the idea of having sex with several strangers on a daily basis, and having to cater to their whims and insecurities and pent-up issues may not quite be an "enjoyable activity."  Perhaps that explains why ...

Flexible hours?  Sure, but I bet it is alot more hours than you might expect.

Think about the number of calls and email contacts you make in the hope of scheduling a visit.  If your really lucky it might be 3 or 4 contacts per visit.  Now look at it from the other side.  A provider has to handle at least that same ratio of serious inquiries per scheduled visit, in addition to crackpots, time-wasters and jerks.  Add to the time required to maintain websites, advertise in escort malls, update photos, keep up an incall location, etc., I doubt this is the lucurative "part-time" job you might think.

If marriage is legalized prostitution, why aren't I getting laid?

sex with you is a very enjoyable activity.

Very few providers have their act together enough to run their business as a consistently profitable enterprise.  Which explains why there are so many agencies.  As mentioned earlier, this is a profession with a limited shelf life and, if a woman is smart, she is setting herself up for a financially feasible life afterwards.  Factor in the risks of LE, injury and the stigma attached and you have a job that not many are cut out for.  

As for the 'very enjoyable activity', well let's look in the mirror guys.  Would you want to fuck the female equivalent of yourselves?

Legal or illegal, high paying, social stigma or not.  
Different professions, vocations and avocations appeal to different personality, physical and emotional types. A person smart enough, disciplined, and diligent enough to go through the schooling to become a Jet fighter pilot could have also chosen being a doctor, or the converse. What a person accepts or doesn’t as job satisfaction, risk, compensation or merely being able to physically fit into the cockpit is all very personal.