There’s a whole lot of (literally) nothing between Afghanistan and anything worth bombing in Russia or China, and the US has military presence much, much closer to the important parts of those countries.

Afghanistan would be good to have in a war with Iran, but I honestly think that the opportunity for that is gone. AFAIK Iraq has gone from being a US client state to nominally independent, and Russia’s plan to prop up the Assad regime worked out very well for them.