Well, it's even worse than a casino-experience for most I'd say.
While throwing tokens down a slot machine one at a time, with very little emotional value attached to each token, imagine having to sit on a treadmill for one hour instead of each token you put in.

It's not so much about the actual "chance" of a huge payout (which is way higher at Steemit), but the "perceived" relationship of work-put-in vs payout rate that gets people frustrated.

Let's say you take 100$ (at 20$ wage/hr that's 5hrs of work) to a casino and sit in front of a 1$ machine. That gives you 100 chances to win and the perception of building up your chance to win the more you put in (which is statistically wrong, but emotions don't care about statistics).
The 5hrs of work you put into earning those 100$ is in your past, so you're not as emotionally attached to it anymore at the time you enter the casino.

Assuming you put the same 5hrs of work into writing 1-2 articles for Steem, the value of your work is emotionally way more "closely attached" to the payout chance, which is basically reduced in the perception to only 1 or 2 chances for "winning".

That's what gets people frustrated way more than if they'd "waste" the same amount of value in a casino.