There is a strong tendency to believe that since it's puppetry and fantasy it's mostly lighter fare for kids.
Especially when you compare it to an "adult" series like GoT full of violence, murder and hot sex.
GoT is in a way the 14-year old's thinks of "being an adult".
When you're 9 years old you will use your magic/superhero powers/giant robot/toy gun to defeat the bad guys. It's a black and white world.
At 14 you're in the "Edgelord" phase where everything you do in your imagination has to be extreme/transgressive/rebellious and you have to look badass doing it.
I'm not saying that the Dark Crystal is Literature Nobel Prize material, but it's very adult in its writing and it's the kind of writing you easily dismiss if your understanding isn't about that of a 14-year old edgelord, as sadly is the case in most "adult" media today.
DCAOR is very human (sic) in its writing. In GoT everyone is an emotional cripple with anything resembling positive emotions being a mere setup for more misery down the line.
People complain that it's all very "touchy feely" saccarine stuff, but look at the aftermath of a disaster or significant emotional event. People need that hug, they need comforting, they are not stoic badasses with the ability to become only stronger the more trauma they accumulate. When you see the characters in the series hug it's genuine emotion, something you don't see often in media these days.
And the writing is very subtle, there are layers to the story. A good example is the way the Gelflings end up treating the Podlings. Prodded by the Skeksis suggestion that they are helpless and stupid they begin to treat them as such, causing great resentment with the Podlings who begin to resist, leading the Gelflings to believe they are incorrigible and need extra supervision, creating more resentment … That's social engineering, creating rifts in a society that used to be inclusive by creating an "us vs them" situation. The Gelflings despise the Podlings for being stupid, the Podlings resent Gelflings for treating them as if they were too stupid to take care of themselves. Divide and conquer.
The Skeksis are able to maintain the illusion of being wise and beneficial even when most people are starting to put question marks to certain things. We see characters surrender to that idea despite evidence to the contrary, actively supporting evil while at the same time rationalizing it to themselves they are doing it for the greater good. "Our rulers are good and wise, what may look evil to some is merely part of a greater picture we cannot see, and we must remain true to that vision no matter what for our leaders are good and wise and cannot make mistakes or cause evil and if they do, it's only going to hurt a minority, who probably deserve it anyway …"
It's not perfect, but it's incredibly well-made, with a rich and detailed world and some really amazing character work.