With the exception of the relationship between gollum and Frodo I don't think there's one jot of maturity in the damn stories. At least not the way you're talking about them. They're fantasy.
Although for the sake of the argument I will concede that maybe you've uncovered an interesting notion - that fantasy is in tension with maturity.
EDIT: Since aluminiumtrioxode liked the post it made me think a bit more about it.
Take reality as a baseline. It's hard to really engage with players/viewers if something is genuinely unreal. So, swords, romances, death. These thinsg are real.
A fantasy sword looks like this:
A mature sword looks like this.
INTERESTINGLY, I wanted a sword with actual blood on it. Something from a crime scene. But googling "sword real blood" brought up ONLY fantasy swords.