It could be true. But if the casino wants to make more and spend more, the casino needs to calculate its budget before starting the promotion so that it is ready to compete with other casinos.
With many casinos operating, it will provide an opportunity for each casino to provide good service to its customers. If the customers are satisfied, they can get higher trust from the customers, increasing their rating among other casinos.
I think many casino have good planning for promoting budget and they not care with how much waste money for getting good traffic and investor with their website, when have some website not active for advertising I think not ability become popular and know by many people. All casino still active for advertising although have million member right now like Stake, BC Game, Rolbit and many casino website never stop for advertising their site, actually with new casino will begin advertising without care how much budget have losing when first time promote their casino website.
Casino should need to realize that spending money on marketing is not wasting money. In fact, it can be a turning point for the gambling business to attain new opportunities through extensive marketing of their casino. The marketing can be in any form like signature campaigns, social media campaigns or giving bonuses to the players etc.