>>213120803honestly, it's because deep inside they know the main institutional and technological foundational seed of their civilization came from baekje and gaya lol. it's kind of a known thing even by the west who study NEA history and esp japanese foundation / state-formation history. they have an ontological seethe and complex towards korea.
that said, both korea and japan's rulers behind the throne dgaf about nationality at all. they're not the public-interfacing CEOs of chaebol or zaibatsu, but similar to the faceless elites who own vanguard, blackrock, and set globohomo initiatives via NGOs, thinktanks, and supernational orgs, the rulers of korea and japan intermarry and dont care at all about japan this, korea that lol.