Why does one learn any language? To communicate with those who understand it. To understand those who communicate in it. To fulfill the prerequisite for occupations based on it.
Japanese, being quite localised, as are its people, is sought chiefly by fans of their creations (ie anime, manga, visual novels, certain martial arts, high tech business). Or for prestige amidst their peers. I've seen several claims that the japanese people in general are loath to indulge amateur / hobbyist foreigners as interlocutors, though there are platforms to find those who do, 'fcourse.
I possess a certain mix of those, as well as a predilection towards their culture and linguistics, mayhap more uncommon amidst the populace.