Thinking about it, I am pretty sure the genre of "seemingly innocent thing aimed at children has a dark secret behind it" is a very culturally US Protestant kind of horror, influenced by the way USian Protestant culture emphasizes making an appearance of clean wholesome happiness even while absolutely horrific things are going on behind closed doors.
I would be extremely shocked if this trope is not in some way a response to a culture that's always talking about how important it is to protect children's innocence while also being the worst perpetrators of child abuse.
If you were lucky enough to have a fairly innocent childhood, you were still probably aware of numerous abuse scandals - perhaps in Hollywood, perhaps in your church. You probably heard something about labor exploitation somewhere. There were numerous ways that you probably learned that dark secrets is just the way of things.
And of course, if you were brought up in this kind of purity culture that claims to care so much about protecting children's innocence, you may have felt violated to some degree when you learned about this stuff.
And if you weren't lucky? Well, then you know on a deep, visceral level that things that seem innocent on the surface are often not.
"Actually, Disneyland is haunted by actual demons that prey on children" is very easy step to take from here.
So like, it is very easy to dismiss this trope as pointless edginess, but thinking it over? I don't think it's really that. I think this trope is speaking to certain lived realities experienced by many people.
