because everything else in this game rocks. but that is it, it kinda useless to bring whole stuff up there - or maybe i'm wrong but at this point i'm completed 64% of game - i finished main story and i'm at about 82% of side missions but still there was no effect of bringing all stuff to mother base except soldiers. After collecting lots of stuff to mother base like gun turrets, emplacement, tanks guns and so on, it kinda don't have any real payoff at mother base except that security unit gets more points.
Mother base was also very cool thing, but i have 1 complaint. Story was good, but since the only Metal Gear game i have played before was 1st part (back in 1998), i didn't understood lots of characters, but that is not a problem, there are plenty of greatly voiced tapes which you can listen even during missions which are informative.
Graphics are gorgeous, game play is amazing. Controls are amazing, it is not even boring to run trough the open world maps on your foot. It has tons of action, sneaking, hiding, crouching and etc. Hands down this is one of the most addictive games i have played in a very long while. "Metal Gear Solid V: The Phantom Pain" (2015) is truly an amazing experience.