Radhika Desai brought up a great point regarding this on the latest Geopolitical Economy podcast: civilian shipbuilding and military shipbuilding are complementary industries. China has both, the US only has one (military). Having both allows greater innovation and technological development as people and resources can move between both. What you may learn in civilian shipbuilding will have applications in military shipbuilding (or in more Marxist terms, practice helps build knowledge and understanding). If you only having military shipbuilding capabilities, in time you may very well lag behind other nations that have both (certain when you’re talking about the scale that China is at).