I think Rick and Morty resonates with people who are struggling with the disillusionments of adolescence: that you aren't as unique or special as you thought,

I think Rick and Morty resonates with people who are struggling with the disillusionments of adolescence: that you aren't as unique or special as you thought, that your parents have problems and concerns that have nothing to do with you, that you're just a lump of matter, and that how people value and treat you is influenced by your practical value to them. It resonates even more with people who would prefer those issues be brought front and center, people who dream of achieving social acceptance but can't swallow the apparent disregard for larger issues that casual society demands. That the powerful and confident Rick openly addresses their fears is validating; that he manages to be blasé about them is reassuring. They are tired of feeling weak next to their peers who seem strong (or, preferably, stupid) enough to work at forging confident and polished versions of themselves that aren't marred by of the horribleness of the world. Rick provides an alternative model of strength that includes adolescent disillusionments front and center instead of sweeping them under the rug; Morty to Rick presents an alternative route to competent adulthood. And of course it seems "nihilistic" to them even though it is nothing of the sort. Nihilism is a natural fascination for socially isolated adolescents, because they feel all of their illusions being stripped away and wonder what will be left when the illusions are gone. (Adolescents who feel socially connected don't feel a gaping nothing waiting to swallow them up when when their childhood illusions are gone. That's why some kids are able to gloss over it as an occasional terror, while it feels like an essential aspect of reality to others.) "Rick and Morty" is leading them along, season by season, to the discovery that there is something left, and, like math, you don't understand it so much as get used to it. The more weird and amazing things you learn, the more you learn that you are going to have an ordinary life even if you also have an extraordinary one, and to go one step further into painful territory, even if you don't.