The online casinos have very strict rules on casino promotions, which were applied due to "bonus abusers", these were players that took some of the free casino bonus money deals or free no deposit casino offers and were unable to ever deposit. Or they might sign up under multiple users names just to collect some free cash this is considered scamming the casinos and the player will be labelled as a bonus abuser. The casinos can take small hits but just like any business they can not keep taking hit after hit. So this is why they do have many rules on any promotions.
Most online casinos have a payout of 97% overall on casino games. So the casinos take is about 3% which out of that 3% they pay marketing expenses, employees ( which most have quite a few ), % to the software company and so on. By the time it is all said and done, the online casinos are not really making that much money per dollar. So casino bonuses are monitored very closely for any type of fraud, cheating or other types of abuse.
long terms loyal slots players receive the best casino promotions, and not only that but they also receive gifts on birthday's and holidays. The casino values the loyal player and shows that in casino promotions. If you do not feel you are being valued enough by a online casino, the best thing is to call or write the casino support and tell them you are unhappy with the treatment you are receiving. If the online casino is a good one they will bend over backwards to keep you as a player.