As far as I can tell, and admittedly this is conjecture based on piecing together a bunch of off-hand comments by official spokespersons and a few industry insiders I talk to regularly, it's because the U.S. decided that everyone needs to use the same exact test. There is some validity to that approach in that it makes the data a lot better for comparison tracking. But, they compounded that somewhat defensible decision to require that everyone uses the same exact test kit. This turned into a disaster when the chosen supplier couldn't produce the reagents in the required time/amount.