Gambling platforms constantly track all their active and inactive users. If users who used to gamble a lot and complete a lot of wagers quit gambling, they are offered various types of bonuses to bring them back to the platform. However, they do not offer bonuses to all inactive users. And they constantly offer various types of offers and bonuses to active and potential gamblers so that they are more motivated and spend more time there by gambling. This is their business and it is natural that they will always try their best to grow their business.
It's a common business and that's why who has wagered the most will get some bonus even if they are inactive. But with some of the bonuses that are given by stake, the factors aren't exposed and so, one could have received some good bonus while the most active with quite decent wagering amount didn't got anything. Though that's really the fact about those inactive ones, I've got some accounts in other casinos too and they constantly send me bonus offers but I never bother to get back.