The promotions they do will also certainly be able to attract more people who will play on their site. It is hoped that with the right promotion, the profits of a site can increase.
Not only does it attract more people but it also encourages their existing players to continue playing. Even if it's only a classic wagering competition there's still a significant increase in wagering activity.
You are right. Therefore, these gambling sites continue to focus on promotions to attract more people, especially if they can provide promotions that attract people and big players. If they can get a lot of big players, that means the gambling site's profits can also be more than before. And providing lots of gambling games will make gambling players feel more comfortable playing on their site.
Because this is what people expect to see on casinos since many believe thay having a good promotion can make people stay on their platform or rather make people stay on what they offer to their gamblers. But as @dothebeats say better RTP is more good to have since this will make the gambler stay since casino will became boring once those promotional stuff ends and for sure if gambler will not see anything like this exist they flee and go to other platform who offers again some nice promotions to them.
With RTP, casinos can allow gamblers to try their luck, but I'm not sure if the promotion from the casino will end because promotion is a tool to develop the casino to be bigger. As long as the casino can provide the best service for its customers, users will not switch to another casino but will use the platform to continue playing gambling. Although users may try other gambling sites, in the end, those users will return to the original casino because he has found comfort in that casino.