Mostly because of the surprise sucker mechanics. You need several runs to figure them out.
Due to my ping being 150ms I cannot do them. But I am sure it would be relatively easy for someone with a 15 ms ping once you figure out the "surprise sucker" mechanics. To their credit, they do show most of the surprise sucker in the variant one. So if you feel stuck in criterion. Do the variants until you do the mechanics perfectly.

The target audience is people that want a challenge. Which is maybe less than 10% of the population. But is nice that is there. Of course, most complain about their rewards as they are not attracted by the challenge, but the rewards.

At the end of day. Do you want a grind game in which you have to treat it as a job as otherwise you wouldn't get the gear needed to continue your adventure? Or do you want a game that respects your time?

I know I would unsub the moment it changes into a grind fest. As I have no time for treating it as a job.