cos the reds left the left side for mounting the rails .
My understanding is that the goal was to leave the entire left side slick so that the rifle could be slung with nothing jabbing in to you.
So it is actually a fairly ergonomic design feature, depending on your perspective.
I actually don't find it slows me down any, so I decided to leave mine along after quite a bit of thought.

I believe its for the same reason the mag release is recessed into the trigger guard: sling mounted on left side where contact with body and clothing happens while carrying. Less chance of dropping the mag (which is suppossed to weigh more than mine do...) or flipping the safety off unnexpectedly. Thats how I figure it anyway. If it was LH and flipped forward for fire, it would be perfect IMO.



























