in GBG, negotiation is limited: even with 0% attrition, you will run out of goods eventually if you keep negotiating.
On the other hand, fighting in GBG is much more sustainable. With 0% attrition, a modest fighting boost, and a good stock of rogues, you can fight as much as you want, without losing much. If you negotiate, you are, by definition, losing stuff.
There are players (yes in low ages) doing thousands of fights every GBG season. Have you ever seen someone do thousands of negotiations in a GBG season? No, because that would cost tens of thousands of goods.