Often the best way for a casino to attract new players is very generous promotions, as people tend to stick to what they know unless there is a very attractive offer. The best casinos will have great welcome offers but also ongoing smaller rewards, it's usually an indicator the casino is doing well and can afford to be quite generous with returning users. I've encountered lots of stingy and tight casinos in the past, they usually end up much lower on my list when choosing where to play - sometimes they never get visited again. A keen gambler can spot the ever so slight differences in the frequency, freebies and payouts between casinos - the more regular the better.
Even when generous promotions are active it is not easy to make money and stay in profit.
I have joined several promotions in the past. Sometimes I made money, sometimes I lost money (and the house won). So, I think that in the end even those generous promotions are not so expensive for the casinos
Don't think about profit or loss, gamble responsibly, gamble only for entertainment, if you still think about profit, it means you put a lot of money at stake and the result is that you will not be willing to lose that money, have fun in gambling, let go of what is lost, enjoy what comes