The KPIs required to win in the search based e-commerce and browsing e-commerce models are different. While Amazon might be laser focused on 1) delivery time 2) SKU count 3) conversion; PDD might be laser focused on 1) user engagement 2) churn 3) SKU count.
However, also remember that the amount of stuff is not finite in the world. In fact, technology has a commoditization effect. It makes more stuff available and hence has a deflationary effect.