I think it is not just about marketing, I mean if they spend this much money on marketing instead they could get much more people, hell they could spend that 1000 dollars to become trending topic on twitter much faster and stay up a lot longer as well.
Marketing plays at least two important roles: The first one is using funds from companies to promote them via marketing with the final objective is to help the company become more popular, and get more users/ customers/ income. The second one is earning income from marketing events and later actitivites in order to self grow marketing. Companies don't be able to provide funds for marketing from years to years. Marketing, itself should be self grown via passive income.
Yeah, the promotions are the important particle here as well, they are making a lot of money for sure but with promotions they are dropping their profitability a bit, they could once again use it to gather more people but instead they are marketing themselves to their own customers which is really amazing. None of these promotions are done to get new users, this is purely for people who are already playing here and trying to stop them from getting bored.
You get to try to do something that is crazy difficult to try and challenge yourself with it which really takes up a bit of time but in the end when you reach the goal than you are happy. That type of thing really shows how awesome stake is, they are not thinking "we already have these, lets try to get new people", they are really working to keep current gamblers happy too.