Online casinos love to reward players, because they know that there is an awful lot of competition out there among establishments of that genre. When they are able to retain a customer, it keeps them ahead of the game, because the nature of the online casino player is characterized by extensive "shopping" around for appetizing offers.
When we talk about a "reward" program, we are talking about one which is roughly akin to the frequent flyer programs you see at airlines. Not an upfront reward like a $33 free sign-up bonus, but compensation for loyalty. That is to say, the more you patronize the operation, the more credit you will get toward rewards. In casinos this manifests itself in the form of comp points that can be redeemed later. The more points one gets, the greater the rewards will be.
Casinos differ as to what a customer has to do to qualify. Sometimes the player is automatically enrolled; sometimes entry into the program only comes if the customer requests it or if they are invited. Often the loyalty program is represented by various levels of attainment. For example, one could go from a Bronze to a Silver to a Gold to a Platinum. Usually, the customer will get more substantial bonuses upon graduating to a higher level or "rank."
It is all designed to keep customers around, naturally. The same can be said of sportsbooks and how they view the "loyalty" issue. The average revenue on a per-player basis is greater in sports than it is in the online casino, but there is also bigger risk, because the average wagers are greater. The games are programmed to bring a certain return in the casino, while the edge a sportsbook may have over a customer is not static, but instead depends on skill level.
The loyalty program that an online sportsbook may have is actually very similar, and may actually be based on one that the casino component of that operation already has. At some of the more established sportsbooks, loyalty points are generated with each wager the customer makes. The points are then redeemed for free bets. For the most part, these plans are geared toward recreational players, as sportsbooks often distinguished between those and the customers they consider to be "sharps" or "pros."
There are other ways in which loyalty is rewarded. It can be argued that reload bonuses are a reward in and of themselves, and there are more than a couple of sportsbooks who have a lifetime bonus for those who make subsequent deposits of a certain minimum amount. A "cash back reward" is not that unusual, coming in the form of "free money" that can be used in conjunction with real money for a wager. The "rollover" (wagering requirement) on a loyalty bonus is always lower than the casino, and generally should be anywhere from 3x to 10x.
One of the differences between the two "products" is that sportsbook loyalty programs are less common than casino loyalty programs. Sportsbook operators understand that loyalty can be a conditional thing, because the very nature of the sports bettors' mentality is that he or she will want to shop for the best odds on any given event; a condition that doesn't really exist as much in the online casino.