I'm not sure where Ford sources its traffic data from, but our Chevy Camaro and our previous BMW had traffic available all the time. Basically streets/highways that have no issues would always show green...and once issues were reported the color would change according to the current traffic flow.
Today we drove the ST 4 times, 1 of those 4 times there was traffic showing on the NAV (all green roads, so no slow downs reported)...the other 3 nothing at all (just the normal grey color for the roads). No matter how far you zoomed out or where you looked on the map. So something definitely isn't working quite right.