Fortunately(?), Trails games aren't as great of an investment short term as Ys. The scripts are huge, the fanbase is smaller outside of Japan, and for Cold Steel 3 in particular there's a two game barrier of entry (And that's not including the giant question mark that is the crossbell duology). If Nisa has the manpower for even a rushed Trails localisation, they would certainly be better off using it elsewhere.
(Also, a major factor in Ys VIII's case is that they promised a PC port that Xseed couldn't provide, from what I remember. Post-Ys VIII Xseed is a different situation, what with the high quality Cold Steel pc port and the upcoming port of the sequel.)