China faces a huge logistical challenge if it wants to rely on Africa for food and ore. Sending cargo ships from South West Africa to East Asia is a long and perilous journey.

Africa itself is an unstable part of the world, the people are not friendly to China, and the population is growing rapidly. Its easy to see the local population turning on Chinese citizens or businesses in the event of some economic or food shortfall.

By contrast the USA basically has all of the resources it needs inside its own country or nearby allies. Many of the 'rare' resources of the world are not particularly rare, they are just too expensive or too environmentally damaging to mine in the West at current prices.

I'm surprised that China doesn't just offer to buy whole sections of Africa, and formally annex the land into its country, and move (voluntarily) the existing African populations as part of the payment terms. For example, the GDP of Mozambique is $16b - China has 200x this value just in USD reserves.