It won't sell well on xb1

Maybe they expect the actual cost of release to be more than what they'll make from it? Like getting it approved by MS etc.? I don't know if they have to pay a fee to get it on the Xbox store or anything like that, maybe?

EDIT: wait no, it still makes no sense cause it's gotten approved by Xbox Japan, and has been released on the Japanese Xbox store. Wut.

No real answer to this unfortunately =. I get the game is niche, but since the xbox version already exists, there's no legitimate reasoning that I can think of.

Xbox already losing third party support in the west? Haha joking, they probably made it for xbox no one bought it in Japan then they realised it was a bad idea soooo nothing for the west

Most of the japanese third party publishers have been doing this. Why? Cause its in their interest to support the product with the most market penetration in both the east and the west. The Xbox brand only has market penetration in the west, and mostly just the US. This may be ok for western publishers but it isn't for eastern/japanese ones. They prefer not to fragment their audience into a system that does not vindicate in the east.

The same reason why certain jrpgs didnt got a ps3 release. The english port would be too costly

Would it really? I was under the impression ports were relatively cheap :O.