Why has the relationship between buyers and suppliers evolved from the original competitive relationship to a win-win partnership?

The statement of competitive relationship is wrong.

Win-win partnership has always been desirable, but now it is increasingly recognized by many people.

The relationship is this:

(1) For suppliers, it is necessary to make a profit. Only when the buyer makes profits for the supplier can the supplier do better and bigger, and the supplier can get more returns in all aspects and give the buyer more preferential treatment.

(2) For the buyer: support the supplier well. The longer the cooperation between the two parties, the higher the trust between the two parties, and the more favorable the price and service the supplier can provide. The more favorable the price you can get, the greater your profit.

In layman's terms, it is gratitude. You (the buyer) gave me (the supplier) money to earn, I earned it steadily, and you still supported me. I naturally want to be grateful, that is, to give you better prices and better services. The lower the cost of your products, the more competitive the products you produce. So that both sides can win.