It's said about brain that, "use it or lose it" — now, question being, do you think if person plays brainless gambling games such as slots, dice for major part of his/her daily routine, will it make him/her dull?
Edit: "brainless" as in playing gambling games that does not require using brain, I thought it was clear especially given examples.
In the first place, why do we gamble? We gamble to excite ourselves, not to become dull and lose motivation.
People become dull not from gambling but from their experience and their surroundings and how people treat them; on the contrary, gambling excites us and takes away our dull moments.
And the only warning we have about gambling is spending too much, not playing too much, and becoming a dull person.