Each map has limited amount of memory for guns. There is no more space left to add more guns.
RAM space is full, and very limited now
Too many tech issues to complete before adding it
RAM space for maps is different than Hard Space for maps. RAM is very full.
Takes too much time to integrate guns into every map
If they prepare the game for more guns before it launches, then there would be no problem at all. But for MW3 they didn’t prepare it.
They don’t want to add more playlists [players w/ new guns ; players without new guns playlist]