I have a different experience. I remember how last year Duelbits ran Christmas box event. Every day users came, open a box a got a prize (1/5/10 coins or 5 free spins if I remember it correctly). Users discussed their results in duelbits topic rather lively. That all created a feeling that more than usually users visited casinos page. I think they also got lucky tickets event, where users get tickets when they wager 100$, so users used free box prizes to wager. All it all duelbits was kinda busy Last Christmas
I gave you my heart 
There are some casinos (also fiat ones) that do something special for Christmas. Most have an advent calander where you get prizes from profit boosts, to betbuilder boosts, to freebets, ... But I agree, the one that Duelbits ran last year, was one of the best ever and I think most people really enjoyed that. But I also think that Betfury will have an event planned for Christmas - New Year.
Fiat casinos can have a similar promotion but its unlikely that we will get attracted by that no matter how good their promotion was because fiat casinos are always demanding for a KYC but we know ourselves, we are here in cryptos because we do not like the idea of centralization or regulations. There are still crypto casinos who have a special promotions on them including Christmas.
It usually lasts for a week or two if I am not mistaken but maybe some will run for the whole month if that casino is big because they already have a sufficient budget for this. Gamblers will surely be busy during the month of December. I am now excited for this.