I'd simply say because the failure rate is incredibly low.

It doesn't matter how "bad" or just "lazy" players are. You can still clear 98.7654321% of content. Net result is it just doesn't matter..

But then because it really doesn't matter players get bored and then drop the game.. another aspect of why player retention is so crap.

Also the learning curve is kinda backwards. They keep dropping the bar lower and lower. Which means instead of the learning curve gradually going up. It goes down down down. Until maybe extremes where there's a bit of a brick wall as it's an almost vertical increase in difficulty and another vertical one to savage.

Sometimes I also think terminology is partly to blame.. when players can play badly but still breeze through an "expert" roulette. It's not really surprising to find they think they can take on an "extreme" I mean the game is telling them they're experts...