I agree with you, basically bonuses have many classifications for both new users and old users, such as cashback or VIP rank bonuses, that will make players interested in staying at the gambling and visiting it every week or even every day.
This is what they want at the end to make players engaged in gambling so they keep wagering on their platform.These bonus give users more interest in particular casino and they are happy.Sometimes we see that codes are sent to inactive players so they get attracted to gambling again and when they start playing they wager more becoming active players so it's all under marketing techniques which is good on both ends.