My reasoning would be:
Unlike the RPGM engines, Wolf RPG is a purely Japanese engine. There is no "proper" English/international version, the documentation is pretty bad, you can't get any non Japanese help, and in general I just do not see much western interest.
There is nothing Wolf RPG can do, RPGM can't do better.
Edit: Before someone corrects me:
Yes "technically" Wolf RPG is an RPGM engine, too, since it was originally cloned from RPGM, but that doesn't really matter considering how different they are now.