Responses
Because Junseo is Jaewon's friend and most important his love confident, but to fit the second role we need to know what is his past, and how he struggle to live until now (this is his major deference with orange hair) Besides is not uncommon that the love interst remains as an mystery not only for MC but to readers as well.
Other than that people just followed the cliché in BL, where at this point it would be obvious that Jaewon changed his feeling to Junseo, but in this story Jaewon has always expressed his feeling towards Karam.
Spoilers
.
.
.
.
.
.
.
.
.
.
.
.
.
.
I've accepted that JaewonXKaram is end game, but why did the author put so much effort into Junseo? She even had a whole flashback arc to fill out his character. In fact, he's more fleshed out that Jaewon is.
Why put all that effort into Junseo if he wasn't the main love interest? At the very least, Junseo deserves a happy ending/spin-off because all fans (whether they root for Karam or not) have become invested in Junseo.