User blog comment:Kogath/Monster Hunter Frontier G8 Discussion/@comment-6050823-20151023122617/@comment-184612-20151026090822

As was said, because Japan made a point of romanizing it; http://www.mhf-g.jp/preview/g9/pc/toridcless.html

This is far from anything new, they're just kinda random about it. As Caboose mentioned, Espinas is actually Esupinasu (エスピナス) but they made a big deal about romanizing it, so we use that.