Is it just the cool thing to hate Nintendo?
Because, ya know, although games can be mature, dark, etc, they're just games. As in entertainment. As in "something to keep you occupied".
Yeah, it's been that way since before I started following Nintendo. Why do you think Nintendoomed is a term?
That said, everyone else DOES have a point about literally everything being a punching bag, it's just that as a Nintendo fan I find it much easier to notice the fact that the media seems to be actively hoping that Nintendo is going to die. And it's not just Polygon either, it's just that they're the most blatant. You can pick up the subtle joy in the Nintendoomed reports from plenty of other news outlets.
And then there's the comment sections on most websites, who seem to either also be rooting for Nintendo to die or else are just having really childish reactions to Nintendo not personally catering to them.
And if these people had enough refinement to look past the cover of a game and research what actually happens in them, a lot of Nintendo games can get shockingly dark sometimes. Their own argument is flawed because they don't care about maturity at all, they just care about muscular manly men with big guns meeting lots of attractive women, starring Hyper-Realistic Blood as itself. These people have all the maturity of a pack of thirteen year olds trying to look cool in front of their peers.