The moral problem may be when the value provided does not match the cost (in this case to the slot user). Just because a slot machine is able to rewire some neural circuitry in the user so that he thinks the value matched the cost...doesn't mean it actually does.

It's as immoral as selling a car for 10x an appropriate price, by not voluntarily revealing a critical flaw. Both involve "cheating" someone based off a sort of information/computation asymmetry.

Addicting someone's brain in way that creates value (e.g. getting them to exercise) is obviously worth a significant cost - and I'm totally ok with someone making a profit on that!