When people go to vegas for a weekend, they might have a number in their head they are willing to gamble. If they dont, then that number is their bank account balance. Then they start flipping coins, and often they keep doing this until they go bust. They rarely cash out when up but they always lose when they go bust. They scale the bets as their bankroll grows. Essentially they are flipping coins for infinite time and just waiting to get a bunch of tails in a row, which is inevitable. The behavioral factors are bigger than the house edge.
The idea that people are rational is also absurd. Some people are driving to the slots _because_ they are depressed. Or they are there for fun but they lose a bunch of hands in a row and tilt and now they're betting everything on a longshot to win it all back and win some because they dont want to self-identify as a 'loser'.
You can only spend so much money on drugs and sex. Gambling is the only vice where you can lose billions. And these days, all you have to do is pull out your phone to place a trade or a bet.