Pregnancy avoidance

Could you tell me why you don't make the "Persona" system (that is, the Clearblue monitor programmed to use as natural birth control) available in the United States? From what I can tell, it's sold in the UK, Germany, Italy, France, the Netherlands, and Scandinavia.

I know the short answer is that it hasn't been FDA-approved, but why not? Has the manufacturer simply never submitted it for approval, or has the FDA rejected it?