it's a bit tricky to think casinos would act against their own incentives
in reality they usually want users to get addicted and gamble more
even if a casino advertise "responsible gambling" (is it even possible?) I'd probably doubt it is for real and not just a PR practice.
Au contraire, addicted gamblers are usually more trouble to them than money, especially for live casinos where they could get bombarded by hate and scandal from addict gamblers, especially in countries where loan sharks are a thing. If anything, there are a couple of houses, especially ones not fully-accredited by their national governments, who promote this type of problem, but most of them would really go to such lengths as kicking gamblers out of the casino if they are observed and confirmed to be addicted to gambling already. Then again, we wouldn't really see this on the daily so it's not going to make it out the news.
That's why I doubt this self-exclusion feature could work for a gambling addict because they wouldn't be using it for their own good.
Instead of using it, if a casino uses this feature automatically on gamblers who use a lot of money to gamble almost every day, those gamblers will just look for other casinos that can allow them to use a lot of money still.
But casinos haven't done it automatically and still give gamblers the option to activate it.
Casinos are also thinking about what if many gamblers activate this feature because it will impact the profits they can get and will reduce their profits.
The self-exclusion feature some casinos offer can be useful but only under very specific circumstances, one of those cases would be when a person which is not addicted to gambling lost a lot of money during a session, then they can implement the self-exclusion feature and keep themselves out from their accounts long enough to think about what they did.
But for those which have a problem controlling their gambling such a feature is useless, because as you mention then they can just open another account in a different casino and gamble there anyway.
True. but this only applies to online casinos. Live casinos do not have this problem AFAIK. The futility of Self-exclusion features against addicted gamblers aren't a good enough reason to not imply them to casinos. The benefits they provide still outweighs the amount of addicted gamblers by a longshot.