Archeology is more difficult than reading. The civilizations which left a literary corpus (oral or written) will have more to speak about than those who didn't.
Archeology also tells us only of what metals people used, what animals they had and what they ate. Whereas literature speaks much more - of the values of those people, which makes it a more attractive target to study.
Finally, even from an archaeological perspective, trade is less interesting than war. So warlike civilizations generate more interest than trade-dominated ones.
Of course this is excluding the fact that christianity made greco-roman culture relatable to most of the west.