Wagering requirements is what make bonuses to look like a waste of time to most gamblers this is because most times we tend to take bonuses without even reading through their terms and conditions and at some point this terms and conditions have a lot to do with the casino withdrawal process even if you make deposits along side the bonuses, this is the reason why some gamblers just choose to avoid taking those bonuses.
I think people wrongly understand what is a welcome bonus. They think its should be free money, when casinos consider welcome bonus to be an imitation of real excitement of playing high stakes/high risk money (as they turn a normal game into a game where you need to risk more or bet own money to get a higher prize).