Here's a good reason: so you can sit off the east coast of China, and hit military targets in their west, without needing fly-over permission from any other countries.
(Yes, there's that little strip of Afganistan that reaches east and touches China, but they're a soviergn country now, and may not want to be sucked in to another superpower war....)
soviergn = sovereign. One of these days I'll be disciplined and always use spell check!