Holy shit, you raise a really good point, and in fact it's something that China has been doing since 2013: The Belt and Road Initiative. They focused on building harbours, bridges, and roads throughout Asia and Africa, with the motive to connect developing countries to China, through good trade relations and lots and lots of debt. We would be able to get a start on one of China's greatest strengths in the modern world almost ten years early. And considering that it's actually within the mandate of our own department, in the interest of encouraging trade and good diplomatic relations, we would be in a position to take advantage of the US' reluctance to rebuild, and assist in the reconstruction of a democratic Afghanistan that we can count on as an ally in the region. We'd then be able to use that as a simultaneous carrot/stick against Pakistan, who can either choose to side with us and reap the benefits of what is going to be the world's premier superpower, or get left behind in the dust as its geographical neighbours thrive under our direction.