I think its fair to assume that as long as you still see any of these website online means that there's probably a good chance they're making some money at least, otherwise they can't stay open for business
Yes they would be making money for sure due to which they are still existing else they would have wind up and nobody would or want to pay money from their pocket for very long. So this is probably assumes and also we need to consider how many new such sites are opening which will help us know if it is profitable or not.
Isn`t that a general rule for all businesses, why would they exist if they don`t make money? Like many other businesses, casinos need more users, just with more users they can earn enough to pay for high security, for new games, a lot of promotions, without users every business will collapse eventually. We don`t need to assume nothing, some casinos share that informations for public, you can check how many users they have, how much profit they make, for example I have some bitdice tokens, every quarter they share informations about last quarter and they pay out dividends depending on that profit to all token holders.