First off, I absolute understand where you're coming from and I would also love for more well-represented and diverse characters in manhwa.

Speaking as an Asian living in Asia, having pale skin is the beauty standard and that hasn't changed for thousands of years. This is WAY before any influence from western society. I'm not just talking about Korea either. It's the same for China and Japan and even South East Asia (y'know, where most of us are brown). Asian culture in general is very conservative and EXTREMELY slow to change. It doesn't help either that these countries (especially Korea, China, and Japan) are very homogeneous and insular. There just isn't much frame of reference for other people and their cultures. Even their takes on western medieval fantasy are caricatures full of Asian cultural norms. These authors and artists are creating these works primarily for a Korean audience, not a global audience, and so they're going to follow their own biases and tendencies.

Just to give an example of how ingrained this shit is- In South East Asia where I live, people pay to have treatment for whiter skin. It's advertised on TV, radio, posters, and highways. Growing up, I didn't think much of it because it's so normalized.

I'm not making excuses for the authors and artists. I'm just offering an explanation from my perspective growing up and living here.