Because if we already open our eyes and see the reality that gambling is luck, we will not be interested anymore since we know we will likely lose due to the house edge they have, especially slots where the house edge is very high.
Although I know that gambling is just based on luck, at least in casino games, I still refuse to believe that sometimes.
I have been gambling for many years, started during the popularity of dice sites, and until now it still has not fully convinced me that it is just pure luck, because if that is already my mindset, casinos will no longer make profit from me.
Although I mostly bet on sports, from time to time when I get bored and want instant results, I do bet on slots.