I would say that users like the OP are the reason why casinos (Bitsler in this case) reduce bonuses. they are obviously right because with the reduction of bonuses or even without any rewards, such users leave the casino (sometimes with so much hate like in this topic)
Well, bonuses and giveaways are there to attract new users and reward loyal players. Unless you know some other goals of these rewards, because that may be understand from your comment?