The typical answer from support would be „The marketing Team is in charge of the Bonus Emails it’s up to them, we are here 24/7 if you have some more questions. We are happy to help“
Most of the bonus emails are not on deposits, they are on wagers.
If you deposit 1.5k and play 1 Bet of BJ they are not seeing you as a value player.
IF you play an wager 15k they see you as a „value“ player -> More Wager more Spins/Bets -> In a long run more profit for the casino. Short bets -> In an out is not where the Casino make long term money.