NGO is a a bit different compared to most international airports in Japan. The vast majority of international passengers seem to be workers from SE Asia, especially Vietnam, with some Japanese who live in the area, and very few tourists. I think Aichi has the highest proportion of foreign residents of all the prefectures, with a lot in Gifu and Shizuoka as well.

So those flights probably aren't going away anytime soon, plus some to China when they return. But I think DTW-NGO has had subsidies from either local governments or auto industry companies for some if not most or all of the time it's been operating so it's not too surprising if it's not otherwise profitable