The Ford parts website very clearly says it’s applicable to ST variants. This also doesn’t explain the lack of the deflector on XLT or Platinum models (see other thread for images).
My engineering judgement leads me to believe Ford is short on these parts for one reason or the other (and getting shorter due to China production slowdown from COVID-19). Parts are prioritized to XLT and Limited models when they have them, then Platinum models, and then ST models (due to importance of fuel economy). These so called “build sheets” that some people claim their dealers are looking at can easily be modified on the assembly line under a deviation type scenario to make it look like the part doesn’t belong. Also, the bumper design on ST models wouldn't have all the holes drilled just for the heck of it since it would add cost on the manufacturing side.