I think it has to do with simple sound. In ost you could hear the impact and whiz of bullets flying all around you, the ricochet sound as they hit the cover you were hiding behind. It may not sound like much, but it really did make you think "Oh sh*t, do I really want to run to that next wall? or will I get shot?" On the other hand, Ro2 may have supression, but in the end it dosn't actually supresss as well as great sound effects.