Why the hell would a country do something for no reason

This is kinda astounding posting and i read it all the time everywhere. On one side we have western imperialists shamelessly and openly looting Africa for centuries, but liberals will suddenly expect China to just do one sided transactions that only cause them loss? And make it the implicit or explicit "both sides bad" argument? It's also usually from the proponents of capitalism and free trade, which is in theory supposed to benefit both sides.