I think that they dont want to take away from Tri's community. If they had done it correctly, they could have increased Tri's fanbase, by making the Wii and 3ds versions compatible. This isnt a crazy idea, Sony is making the Vita and PS3 compatible to a certain extent. Jurassic85
The reason why Sony could do it is because the PSP and PS3 versions of Portable 3rd are carbon copies of one another. Tri G has almost double the number of monsters compared to Tri, one new area, lots of new armors and new weapon classes.