Deposit bonus mightn't be a gift to you because you feel you have to do something to get it but we have other bonuses that can be classified as a gift because your money isn't involved in getting those bonus like the welcome bonuses that casino gives to new users.
When you receive deposit bonuses, it can also be classified as gifts or reward for completing a tasks which says the same thing to me. You're not buying the bonus with your money so why aren't you concerning it a gift, this could also be a sign of entitlement.
All bonuses could have been free but we know they'll be abused by those that just want to make free money without putting in effort by betting. The casinos are only putting this requirement to prevent them from paying unethical people and going bankrupt.
Can you please point me toward a casino that gives a welcome bonus to new users that they can withdraw and have in their wallets? You can find none because even the welcome bonuses are given for you to gamble on the platform and have some terms and conditions which you will need to meet if you win something and want to withdraw, so I don't really think that we can consider that being a gift as a gift that is given to us is ours to have without any conditions bound with it.
And deposit bonuses cannot be classified as gifts because they are not given to you for free but are given to you as a bonus for spending your money, and a gift isn't what you get on top of what you spend but it is something that is given to you without a condition or anything.