I think part of it is that black hair is super common in South Korea. Paired up with the "Justin Bieber" bob is really popular with kpop idols.
I guess a similarity is how male leaders in the 90s sort of looked like this

And I wish I could find that meme of characters that look like Tom Holland, with the babyboy face, large nose, and ears that stick out.
I have like half face blindness and I honestly can't tell most brown hair white male leads apart.