Many gambling sites have deposit bonuses.
However, if you receive the deposit bonus, there is a condition for withdrawal.
For example, 10 times the deposit amount, etc.
What is the reasonable condition you think?
The gambling sites give bonus for a reason. They want to attract the customers and also want the gamblers wager at their sites. that's the reason we will see that none of these bonus are withdrawable unless you invest some amount in the site. If there were free bonus without any restrictions then everyone will make many new accounts and keep on collecting the bonuses.