Not only ldols but every public figure hardly comes out in Korea. There are various reasons for this and a big one is that a sizable chunk of SK's population is Christian and most of them having hard stuck right wing political views. How it came to this is rather complicated (trust me it's not that simple like they worship western value's blindly because U.S influence) but they are very aggressive condemning LGBT movement using their religious beliefs. Also another thing that I personally think that impacted this is that the first person came out public as a gay men and got famous(Hong suk cheon) often used his identity as a comedic gig and that kinda ruined the initiative to take this issue seriously. Just adding context.