I can say that, if a casino is not running a signature ad campaign and also does not gave any form of advertising running on other places, if they have a new product or feature they want to let their players know of, they can simply post about the new product or feature on their announcements threads and their social handles, this can still pass the message if they have a lot of their customers paying attention to their updates.
Yes it is true there will be some ways but it will not last long and can really make the casino grow more in getting more customers, moreover if only rely on feature updates or others with messages sent via email or on social media accounts it is not so effective in getting the attraction of new gamblers.
Still advertising specifically in the long term with some cooperation with certain parties will remain the most dominant and has been proven in real terms, some big casino that are still popular have special cooperation such as with affiliates, and also some sponsors for sporting events and there are still many more including with signature campaigns on this forum.