I'm pretty sure it's not so much the skin but the fact that it's becoming more apparent what Deca is doing. These events aren't really for everyone, just people who want to/can sink a ton of money into the game.

Look at the halloween event and how it's set up, they limited the ways to obtain the candy which in itself isn't a bad thing. But when you consider they made the new dungeon the best way to collect candy and made it's drop rate pretty low(I've honestly seen more public tombs), it's pretty obvious they are doing. They are trying to funnel people into buying the keys, just like they try to get people to waste gold on the mystery boxes for mystery box exclusive items.

I've enjoyed the chest events and how they always have super low drop rates(to the point of no one getting anything through multiple dungeons) even though it requires a good amount of effort to clear some of these dungeons and they always have key sales.

They don't care, most of their released content will probably be stuff more like this, minimal effort, maximum profit with sprinkles of dungeons like "the sewers" in between to seem legit. There is nothing wrong with profit except when you try to exploit people to gain it.