That's what makes it so good. They've learned from Lost, where they teased that there was an explanation for everything, and then it collapsed under the weight of everyone's expectations. Instead, it just happened, they were very clear that it will NEVER be explained, and that helps you get into the heads of the characters, because they're so fucked up by it.
The episode was anchored around a birthday party where it seemed like everyone was in a good place... and then, the mask falls off and you see how completely bonkers everyone is.
Also, this should probably be moved to the current TV show child board.