In "normal" firefights, where distance of engagements vary from -50m to about +200m, there is no need for a rifle with great accuracy, but if you can choose your weapon, in CQB zone you'll mostly pick up a short rifle, which gives you all the firepower you need.
Ok, SMGs will have less recoil, but if I have to use almost an entire mag to eliminate a single enemy, I would have to carry a lot of mags, thus increasing my bulk.
On the contrary, if I am meant to engage enemies at higher distances, which is more than 300m, I will use a rifle which I know has good/great accuracy (which requires a longer barrel).
Oh, XClutchX: great pieces of work!