Is any of this much different from pop boy bands of the 00's? You make generic, catchy songs that are hard to resist. Then have a group of four or five attractive teens perform the song. And then Highlight each individual so people form a parasocial relationship with the band members. The fanaticism follows quite easily from there.
These days, the members get involved more in every facet, including doing their own choreography & writing / producing their own songs.
Seventeen in particular pushed their choreography to the point where it feels like they made it a new sub-genre. Kinda feels like a concentrated Broadway show.