Unfortunately that's just the way it works. WGT is a business and charges more for the fancier equipment that you're buying. They have no obligation to provide an avenue for "free" credits at all. They already provide free equipment and free games.
Your credits would go a lot further if you scaled back to stocking up on some of the WGT or Srixon balls instead of going right for the expensive Nike's in your bag.
An added benefit to using a little bit lower end ball is that you will really develop your skill level. Using a ball without added distance helps you with your long irons before you advance to a tier where it is forced on you. Same thing with a little less spin. Learn where to land the ball on the greens or run the ball up instead of trying to throw darts at the pin.