From the Simpsons:
Man: How many of you kids would like Itchy & Scratchy to deal with real-life problems, like the ones you face every day?
Kids: [clamoring] Oh, yeah! I would! Great idea! Yeah, that’s it!
Man: And who would like to see them do just the opposite – getting into far-out situations involving robots and magic powers?
Kids: [clamoring] Me! Yeah! Oh, cool! Yeah, that’s what I want!
Man: So, you want a realistic, down-to-earth show… that’s completely off-the-wall and swarming with magic robots?
This is Neon Genesis Evangelion. Some emo kids deal with their own problems and then have to save the world with giant robots. Other anime might be mature, but this one seemed to be squarely aimed at kids who didn’t want to be talked down to. I don’t think it’s anywhere as deep or well-plotted as it wanted to be, but it was definitely trying and teens respond well to that. It doesn’t hurt that it really presented a very different kind of giant robot show than had existed in the past and introduced some classic character designs and well animated destruction.