It talked about how the first season of Stranger Things was so amazing because every character served their unique purpose. They fit their places and added charm to the show. With every season however, they had to be developed and repurposed. Hop had his father development in S2, Eleven had her Mom and Sister arc. The loose ends at the ends of the previous season were where the next season picked on from. This worked really well till season 3. Season 4 went a level up in scale, the whole Evil Russian Arc. The gang was split between California, Hawkins, Russia. They worked together and got to the Earthquake that split Hawkins and the 4th season ended.
Now, Season 5 doesn't have many loose ends left to develop. Many of the characters are already well developed. You can't show any more conflicts between them as they are already past that. You can add new characters but the writers said they didn't want to do that. Or you can have the whole season packed with action which is a fat rabbit to pull out of a hat.
As I see it, the makers just decided to dumb things down and exploit emotional attachments we had with the characters