Those kpop lyrics are nothing special. And those rap lyrics are not representative of all rap.
Also you should realize that one of the biggest reasons why people like rap is the overblown and often bragadocious lyrics. Grotesque lyrics are just a part of the appeal of horrorcore, memphis and other rap subgenres.
Just like simmiliar lyrics are a big part of the appeal of stuff like goregrind, slam death metal and other such genres. It is not supposed to be any deep comentary. Just exaggerated brutality for the sake of exaggerated brutality.