Two potential issues. Right now under Japanese government (admittedly highly odd) rules all flights from China and Korea has to come in to Narita or Kansai International, and JAL has not been operating GMP flights since the beginning of the pandemic. I notice that for May the adjusted timetable for Seoul has a ti be announced sticker on it, which is usually an indicator that they expect a change to the past periods of adjusted timetable, ie something is probably going to be operated from May forward.

June schedule is the unadjusted schedule still.