I have written lengthy paragraphs explaining the relationship between: nutrition; grains and cereals; man-power:calorie-yield efficiency; foodSurplus->specialists->development; agriculture and domestication; storage and preservation; size and units of governance; harvest and livestock distribution, etc... But then I realized, nobody is going to be interested in that. Even if they were interested, they could get a more comprehensive explanation from books, articles and journals.

So, I'll leave it to this:

It's illogical to point to the "lack of food-surplus" as the direct source of "lack of technological development" because the universe of asoiaf has the by-product of food surplus: tribes, towns, nations, kingdoms. The universe of asoiaf have the components: They have writing, sailing, communication, organized armies, centralized government, religion, specialists, industries, etc. Food surplus leads to OVERALL DEVELOPMENT, not just technological development.

The question still remains, why is there technological stagnation/retardation?

Food->Technology is a far-off correlation. Isn't there a closer correlation to technological advancement? What sits closer to technological development? Wouldn't it be Knowledge?

The issue with the Dispersion of Knowledge stems from the Maesters and the Citadel