Even a lot of land-based casino's allow for people to cancel a self exclusion within 24 hours... Or to return after 90 days.
There is no absolutely perfect way for Casino's to do this.
At some point, it still ultimately relies on you doing your part in avoiding gambling. For example, you could always create a new account using a VPN or a new IP address. Would that too be the Casino's fault? It wouldn't.
Land-based casinos actually make it a lot easier to feel that you've been banned though since you visiting them slaps you in the face that you're, well, banned from entering until said so. Online casinos provide way too much accessibility that excluding yourself from one may or may not actually be helpful due to other casinos existing all the same. It all ends up with you being responsible for it yourself as you said, though I guess having a centralized system for gambling might help this kind of problem out, where all users are registered in one major database, so that exclusion from one could also apply to any other existing registered casino.
At the end of the day people need to take responsibility for their actions, one of the things that I do not like about modern psychology is that they are always try to give their patient a get out of jail free card and somehow blame someone else for their problems.
As I said, if a casino offers a feature and then fails to make good on their promise then that is simply bad customer service, however people need to always be responsible for their mistakes and recognize that if they had not gotten addicted to gambling then they will be addicted to something else, so they need to improve themselves to the point they can beat their gambling addiction.