WGT is in business to make money, shockingly enough. They will charge what they think they need to in order to turn a good profit. Larger purses in free tournaments would mean people would buy fewer credits, and/or acquire fewer from sponsored activities, which in turn would mean less income for WGT.
Of course almost every player wants to play as much as possible with minimal expenditure of money or time spent on sponsored activities, and WGT would like to be able to earn as much money as possible from each player. This is simple economics.
Frankly, your suggestion isn't the least bit constructive.