Most of us are aware how geoblocks are one more reason people nudge towards piracy. Well, I didn't knew that companies imposed geoblocks even on free content.
If a distributor for Korean movies in the US was the only company that subtitled a movie in Spanish for example, then Netflix would have to make a deal with them to include subtitles for every region. It might be that the distributor themselves may not have the rights to distribute those subtitles outside the US as well.