Why is the AT not the Primary Weapon?

I just picked up a rifle in Tunisia, and my AT guy dropped his fully loaded AT rifle, I know I was not thinking, but it made we wonder why, as the Primary Role the AT rifle is not the Primary Weapon ?

I can Reload it after all.

So I dont think they’re worried about me spamming to many AT rifle rounds down range.

If you drop your rifle, it become a primary weapon, the system is stupid