In Pocker there is a clear correlation between your actions and your results. The other people are clearly better than you are and most get the hint after a while. It's also slow enough so you get some time to think
Engineered randomness (like slot machines or loot boxes) use the means of technology and presentation to dangle that bit price juuust outside your reach. They also use flashy lights and fast paced games to get you in the "zone" of gambling more and longer.