You ever notice how in 99% of the movies futuristic timelines, the guns all look nice, but they shoot like shit and are almost useless? Its like everyone is always playing halo and it takes a full clip to kill anything.
i think it more of an eye candy thing. who would wanna watch a movie where everyone is killing everything in one shot? don't you wanna see the fire exploding from the end of the barrel? the sound of all the bullet casings hitting the ground below. that intense moment where there's a chance they are gonna get killed or shot cause they have to reload and they dropped the clip. its all about keep peoples attention.
The two things I would most love to see are a) the movie just randomly ending because a stray bullet hit the main protagonist or antagonist at a random, totally unexpected, time and killed him or b) people dying as they should (5 bullets to the chest don't just knock you over) and trained soldiers not missing a whole clip at point blank