Of course, this would only be effective if a gambler used one account in one casino. If a gambler, after each limit, moves from one casino to another, such restrictions make no sense.
Well, if a gambler has a few accounts at the same casino, it is shortsighted because it's already multi-accounting. In this case, a gambler risks running into a permanent ban and loss of funds.
Casino A can't do anything about a player having accounts on Casinos B and C. That's not their concern. What they can and should be focusing on is their own platform. If the set limits prevent the player from further gambling activities on their site and the player goes elsewhere, everything that happens afterwards is the responsibility of the player.
On the subject of multiple accounts. Casinos have ways to recognize multi-account holders and abusers, but such checks are conducted during withdrawals or account verifications. Abusers may think they have gotten away with it because their activities weren't recognized early on, but it can blow up in their face any day.
You are absolutely right with everything that you said, and commenting on the first paragraph, just as you have said, a casino has not say if a gambler decide to have accounts on other casinos around, what I think each of this casinos should focus on is to make sure to always improve and offer the best of services for the customers enjoyment and satisfaction, it is often said in my place that a man who is well feed in the house hardly goes outside to eat, so also if a gambler is completely and absolutely satisfied with the services of a casino and love the experience there, he or she will hardly look the way of other casinos if those other casino have nothing new to offer the gambler.
So one way to retain gamblers and keep them locked on a casino is for the casino to be the best, limiting gamblers will only drive them to other casinos as we all have seen the case to be over the years.