Duelbits has a lot of promotion if you will go to there promotion page. This 5$ is exclusive for long time offline player to attract them to go back playing in the casino. Actual other casino offer this kind of promotion but in different way like free bet and free spin which I saw on fortunejack and sportsbet promotion email. You can check out too the Ace loyalty rewards because they are giving instant bonus base on the amount that you wager in the casino
I have also seen casinos having this strategy to retain their inactive customers as when you give them free opportunity to play once the interest come back and then you also wager some amount from yourself.This $5 free bonus to the players is also good approach from the duelbits team.