Makes sense since Ys VIII sold poorly on the Switch. Maybe they'll port this one after a year as well but nice addition for the PS4. Falcom knows where their fanbase is for these games, much like the Trails games. Sony and Falcom have a pretty good relationship and history with these types of franchises.
Poorly in japan, worldwide it sold pretty fine. And it was a late port, a same-day release would look a bit different. Also this time there will probably no PSV-version.