Funny that you should mention naval size. China might have a "large" navy, in terms of number of vessels, but in terms of raw naval power, what rank does China have?
On the other hand, China's nuclear force may be small compared to US and Russia, but it does its job quite adequately. Why should China repeat Russia's mistake of keeping huge stocks of nuclear weapons that are expensive to maintain, and extremely difficult to dispose of?
The second artillery also has conventional missiles, and I don't think the numbers of those are small.