I was hoping that it was just being held back because it's a ridiculously dumb idea for a movie.
Suspension of disbelief doesn't come in to it here, unless the Chinese armed forces have access to magical wizards who can transport their troops in to the United States because their Navy certainly isn't up to the job.
You see, invading the United States would involve somehow getting past their navy - which is larger than the next
thirteen navies combined - and having enough ships left afterwards to land the troops (which would have to number in the millions), equipment and supplies necessary to successfully invade a country of 260m people where civilian gun ownership is common.