Usually sites that gives free bonuses hardly ever payout what you've profited, people who can withdraw are very lucky. That's why i don't like free deposit bonuses because instead making chunks of money you'll get accused from account irregularities with no proof that you've committed such activities.
I believe the OP just got lucky because those sites don't have much traffic.
So they are giving some leeway to these players.
However, if he won thousands of dollars from this, I believe it will be a different scenario.
Just like one site that I've came across, the player won large amount just by using their free coins.
And they are not amenable to give it to the player. So I think the scenario will be different if the OP raked a lot of money.