Bonuses are usually done because gambling sites wanted to attract more gamblers with this. Sites didnt made this just to give away money but they also have it seen in the future. You cannot gambling in just depending on the bonuses you collected because sites knows it can happen and they can possibly have a system which has greater odds if you put your bonus money.
Indeed, we can't rely on bonuses that give on gambling site even if it is for attracting people that may encourage in doing gambling. Bonuses and affiliates I don't waste my time on these kinds of earning because they only give a small amount and it might need a minimum withdrawal. Deposit your own and enjoy have fun don't chase on a small number of bonuses.
Yes, with the smaller bonus it is impossible for us to make higher amounts through gambling, in order to attract people they will give a very tiny bonus to the investors. With the deposit bonus, it is impossible for us to make a good profit. So it is good to invest your own money for gambling.