Because SEGA could not end it with just the second form. SoA (and maybe SoJ helping or whatever) would not just have to think of another appearance, but also another regular attack (at the very least). People would more than likely find out and it would just be too drastic a change.
Tanith I agree. They are definitely not taken from shoulder level, that's for sure. >.> (sorry sorry sorry... if that even makes sense!) They are supposed to be aliens, but I guess just too similar yet dissimilar...
Anyway check those screens out, the bottom part. I guess you could rename your characters but SoA disabled that feature.
