maybe they did such a big promotion month in the past to have some extra attention on their website
I could bet that december is a better month than january too for gambling websites, more money in people's hands and all... January is probably a bit slower in terms of earnings.
A lot of casinos do something when there is a big event like Christmas but I would like to see the difference in amount of wager between December and the other months. I think in July/August when a lot of people take their summer holiday, the activity will be a lot less.
Although that can be a possible propeller to increase in wager volume and trafics to the casino, but then also, we have what we call the mood of players and what tends to make people gamble more, and anything that makes us stay in one place is a monitor to increased gambling.