Halo 2'questions

In halo 2, why was the ma5b or ma5c assault rifle never included? Subtle changes from halo CE to Halo 2 always made me wonder. There were also the differences in the automag pistol. (Loved the halo 2 pistol) why were thoes this changed?

Bungie liked to change up the weapons between games. Perhaps they thought a magnum with a scope was too powerful although I was happy when it returned in ODST and Reach. The SMG took the place of the Assault rifle in Halo 2, I think, to allow at least two human weapons that could be dual wielded. Dual wielded SMG’s are very effective against Elites up close.