It is a shame that bonuses are not really considered seriously by the sites, as if they were something optional or just a gesture of good-will. A bonus is an agreement for someone influencing their friends or other people and promoting you image. That is not free and it takes time so if the site then scams or re-thinks is reason enough to provide public feedback and negative trust.
You are right the referral bonuses are payments for individual efforts at the end of the month and the casino is not in any way doing you a favour and they are paying you for your efforts because is not an easy task to build a referee network and they must also be actively watered for you to be able to get a good amount in referral earnings and commission and this is more also about teamwork.
So referral system takes a lot of participants but the only way the casino may do play a favour is when the bonus comes in the form of a welcome bonus, that way the casino is doing the player a favour but even at that casino still imposes higher wagering requirements on welcome bonuses.