What about it? It's called South China Sea for a reason. BTW, many countries are disputing over parts of it, not just China.
By contrast, US has been occupying parts of Syria and Cuba. It overtly seeks to take control of Greenland. It has 800 military bases around the globe; in most cases, de facto occupying a country.
Is it a rhetorical question? In my opinion this dispute is closely tied with Taiwan claim. When China gets Taiwan - it gets most of the critical area containing shipping lines and oil/gas fields.