A local friend told me it’s because the ground is not stable enough for underground metro; but given the bus interval I think there’s not much demand for public transport to begin with. That may have something to do with Ulsan having the world’s largest car factory, sparse population distribution and cheap pricing for second hand car (around a month of student salary for a decent one).
considering xkcd 1200, the same could be said for the flatpak/snap trust model