The offer isn't bad when you compare it to traditional welcome bonuses. Winnings are capped at $100 because it's almost a no wager bonus. If you claimed a standard welcome bonus you would be looking at wagering requirements of 30x or more. Here it's only 1x on whatever you win before you can withdraw.
There is less wagering requirement, only 1x so it's more possible for users to turn their bets to wins and can withdraw won money and no gamblers want to wager 30x than wager 1x to withdraw money.
The thing I personally don't like about it is the requirement that you can only wager your winnings from the free spins on selected slot games. If they allowed players to play any games of their choosing, then it would be even better, but it would also drastically increase the percentage of players who turn their bonus money into real money.
Exactly, with easier wagering requirement, only 1x, Jack.com knows that it can be easily achieved by users, and if they don't set up a low cap for user winning and withdrawal from that, their casino treasury will be drained.
The cap is set to make sure that Jack.com can give easy and attractive offer to user community while it won't contain too much risk for their business. It's simply to understand their approach because online business is to make money for its owners, not to lose money to users.
