One would think this is one of the most painless ways to learn history! Isn't that a noble goal in and of itself?! Especially when it's the story of probably the greatest king in Korean history?!
Well considering he is one of the most important kings in Korean history, Koreans have probably been taught about Sejong all throughout school and I can imagine a burn-out on the subject. Plus, this isn't the first time Sejong was in a historical drama.