In order to run a campaign, you must have good website, good products in case of gambling sites, products are their games, good promotions during campaign time. All of them will result in attraction of the gambling site and success of the campaign will be reflected by new users, new bet value daily, weekly or monthly.
The success of campaign will create new budget for gambling site to continue it longer. If success continues, they will expand their campaign more (bigger and longer). It is exactly what we have seen with Roobet and their signature campaign and different contests in the forum.
But, if you are doing marketing and have a good website, good promotions, good bonuses, good casino then everything will go according to the play. This is why when you are doing marketing it all depends on what you are trying to attract people into. As a person who has been working in marketing for over 6 years, I worked in both sides I know that money doesn't solve all problems, it just enlarges them.