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.
It's a cycle: Promotions > New users > Higher income > More funds allocate for promotions > Cycle repeats again and again. In addition, you are right that promotions run not only to catch eyeballs of potential new users, and have new users to increase total income for the platform, but also to keep most of current users to keep using the sites. Over time, the site might have loyal users, and it's amazing to build up a strong community like this, partially via promotions.
I do not think its that easy, for example if there are promotions and it doesn't return as many users and wagered amounts as the promotion gives out then you are getting only a small number of users back and small numbers of wagered amount back and you do not know the life cycle of how much that new user will spend until the next promotion, maybe he will keep playing and lose hundreds of coins or maybe he will stop and not play anymore.
It is a dice roll on stakes part if you ask me, yes there is a chance they could profit from this promotions type of marketing but I believe they may not profit from it as well and there is no way of knowing which one is true until enough time passes. I think these promotions helps out getting more wagered from current users more than new users if you ask me.