Look at the population of Japan, Jetstar, Peach, AA tried...
It's a massive market not just 40 320s worth but 100's, it's educating the local population that it's cheap to fly* compared to old times. LCC Japan are cheaper than the Shinkansen (bullet train for the belligerent). It's a growing learning market.
I'm surprised there has been no Jestar India or Jestar Indonesua yet..... :
