I'm with you there! When I asked something similar on an earlier chapter someone told me most of the frustration was from the main storyline being put on hold. I do agree they could have done the second couple as series of side stories, but I like the second couple and honestly am so sick of them dragging out the main storyline that it made me not care as much about the main couple. ┑( ̄Д  ̄)┍ Love the bottom but not into the "mental anguish" of the top anymore.
Its probably because the plot is so interesting that it gets a little frustrating when it moves over to the second couple because they don't really add much to the overall plot or add much substance. I like them but im so invested in the story that I would prefer less of them too, specifically at this point in the story where things are unraveling.

I’ve just read the latest chapter and some of the comments below and all I can see is how almost everybody hate seeing the second couple. ╥﹏╥
Sure, each time it gets really deep and exciting about the first couple we switch to the second one for about few chapters (it’s not the first time either and I fully understand the frustration for waiting a whole week for new chapters and this back and forth switching in the story isn’t the best either ┑( ̄Д  ̄)┍). I don’t know if it’s only me but I honestly enjoy Park Hyunmins and Go Jae Pils chapters. Sure, it’s not the healthiest relationship either but if we are being honest, the whole story is messed up… So is the only issue for hating on the second couple the frustration for not getting enough context of the first one or what seems to be the issue?
If anybody read the complete text, please understand that I’m not trying to attack anybody with my opinion. If you prefer the first couple, that is totally fine. I love them too for their own psychologic fucked up things. But I find it so sad to see people hating on the other couples and the creator. ┗( T﹏T )┛