Dear it is free spins. If you think free spins give bigger amount so it is not possible.
In betting you bet your amount than you get the reward. In this if you win than you will get your amount.
But free spins are free and in this case you will never get big amount and not sure that the withdraw will be possible or not.
I don't agree with the word " not possible". to be honest, free spins do not promise 100% winnings, i know that. But for some chances, you can get a lot of money from free spins feature.
I agree with your statement that the reward is can be smaller than the total amount of bets we make when we get free spins, but that doesn't mean it's impossible to get a lot of money. It all depends on your luck when you get these features.