Why were kushi tes so eager to trade their gold for egypt's grain?

The main goods around the trade between the Kush and the Egyptians were the grains and gold. The Kush provided the Egyptians with gold, while the Egyptians provided the Kush with grain. The reasons for this were that the Kush had gold in abundance, and the Egyptians highly valued gold and they used it a lot. On the other hand, the Egyptians produced a lot of grain, while the Kush were not able to produce in such high amounts, so they obtained food from Egypt. It was a win-win for both sides, as Egypt was getting the metal that they valued the most, while the Kush were getting food in return which they lacked otherwise.

i think its the outcome of people's preferences.

yes they have. but is this a true false question? if it is, the answer is true.