Seriously, why is it that the enemies in games always have the best guns, but they leave them laying on the ground?

I mean, really. I'm running around with a semi-automatic shotgun, a sine wave gun, a space-age magnum, a frigging laser beam and an anti-tank rifle that I use against infantry. And I found all of them besides the magnum, which was given to me.

You'd think the savior of the galaxy wouldn't need to scrounge weapons off the ground.