[Dr Winston O Boogie jr]

I think that you're answering your own question. You and a thousand or so other people paid $10 a head to see these guys bowl. That's $10,000. The rest of the purse has to come from a sponsor. How many companies are willing to put up $50,000 to get their message in front of 1,000 people?
As to your statement that these guys bowl as well as they did when they were on the regular tour, I sincerely doubt that. If they did, they would be entering regular tour events and bowling for the big bucks.
Golf attracts many more spectators and television contracts than bowling does. That is why the purses are higher.
Even in golf, the purses for the Senior Tour, LPGA Tour, European Tour or Web.com Tour are lower than the PGA Tour simply because they attract fewer spectators and/or televisions viewers.
You have to remember that all professional and some college sports are just big business. The reason that exist is to sell products. The reason that baseball, football and golf are on television is that companies are willing to pay a lot of money to advertise during these games. That's where the money comes from. There is simply not enough interest in watching bowling to entice sponsors to spend their money.
Don't forget, if a sponsor puts up $2 million to sponsor a golf tournament they are expecting that it will result in more than $2 million in profits. Why else would they do it?