Some of the problems you mention are oft-recurring ones in YA, especially the newer TV adaptations of existing SF and Fantasy franchises. Cheesy dialogue, focusing on teen angst and hookup culture, and in general poor writing with little regard for the source material. What I mean by the latter is that they build the world to suit the story, which rarely works. In contrast, in good SF and Fantasy, the world, the story, the people in it and the events around them all work together.
But the mistake that they seem to make repeatedly is thinking that the YA style has wide appeal with younger people. It doesn't - not when it is applied to existing franchises like this. The reception by (young) fans, and viewership figures, confirm that. Young people don't want everything to be YA, they want to be taken seriously and be served serious entertainment fare as well.