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.
It seems the K-pop industry has come up with a somewhat repeatable machine for churning out these bands: they manage everything from scouting young talent and training them, writing the songs, merch, events, etc?
It's no different to what has been happening in the music industry for decades. Many of the most popular pop songs are written by third parties and the recording companies will often pair artists with experienced producers and tour managers.
The popularity of K-pop is more an artefact of the US mainstream favouring individual rap/hip-hop over dance-centric boy/girl bands and leaving a large opening in the market.