User blog comment:The Milkman/Hearthfire Announcement: My Take/@comment-3186821-20120831203037/@comment-5280592-20120831213714

To the original question on why Rome used them:

"..martial artists use spears differently than soldiers do. A martial artist trains to fight one-on-one or several-on-one battles, under which circumstances a spear is an awkward weapon; it's tricky to manipulate and is useless if your opponent gets inside it. A soldier trains to stand in line, obey orders, have discipline and not have to defend himself from more than one direction—unless his formation has crumbled, at which point he's got much larger problems than the fact that he doesn't know how to use his spear in single combat."

Anything more complicated than just a a sharpened stick would require a complete overhaul of not only combat but A.I. as well. More people would be distracted by everything to look at when a metal blade is rushing right into thier torso than do what the current A.I. does. I shall find a video if this explanation is too confusing.