BassAssassin, this is a very good question.
The pros have fished both circuits as have others trying to get into the subsequent Classics.
In his book, Fishing on the Edge, by Ike here is what he says about being a professional bass fisherman. May I suggest you obtain the book and enjoy it. Great and easy to read with some excellent fishing suggestions and tips.
Page 183 - We're not as rich as you think we are.
Many people don't understand that bass fishing isn't baseball or basketball. I'm lucky and grateful to be as financially successful as almost anyone on the tour, but Kevin Garnett and I don't exactly shop together, you know? The majority of the guys on tour are scraping by, existing year-to-year, even tournament-to-tournament, often while paying most or even all expenses out of pocket. If you see a sponsor's patch, it may just be for a discount on equipment, not a giant check. Many boat sponsorships require an angler to pay fof the boat when the season's over. My point? Fishing's a rough lifestyle, and only a lucky few ever get rich.
Ike goes on in the book to say that it is very expensive to be a bass professional and pay your entry fees, gas, insurance, taxes on the boat, motor and trailer, keep your equipment in good shape, purchase line and pay off the boat loan. Throw in food, lodging and being away from your family for weeks at a time you can see that being a pro bass fisherman is not an easy career.
So fishing both tournament trails across the USA can be too expensive for your average bass pro. So they focus on either the FLW or B.A.S.S trails and hope for the best.
I suggest everyone get Ike's book and read it. He has some good insights into professional bass fishing. Ike discusses sponsorship which is very eye opening.