"why would innovations discovered by a single AI not spread soon to the others, and why would a non-friendly AI not use those innovations to trade, instead of war?"

One of Elizer's central (and I think, indisputable) claims is that a hand-made AI, after going recursive self-improvement, could be powerful in the real world while being WILDLY unpredictable in its actions. It doesn't have to be economically rational.

Given a paperclip-manufacturing AI, busily converting earth into grey goo into paperclips, there's no reason to believe we could communicate with it well enough to offer to help.