The M Sport isn't designed for taking to the track in any serious way, maybe a quick run around but it's not a track car, seriously. You need to prep the car before contemplating that -- M Performance at a minimum. The M Sport is more about a cosmetic package that is sportier in looks, not performance.
No one here knows for sure, but I suspect it's really about keeping the cost down. The M Sport cars in the US are already slightly lower spec'ed than other countries, there is a pattern emerging. Also, NBT Nav isn't included in any US F30 except the AH3, another example of getting away with the minimum spec in order to reach a price point.
F30 335i M-Sport with Estoril Blue II, M Performance Aero Kit, M Performance Exhaust, M Performance PPK, Adaptive Suspension, Variable Sport Steering, Revised NBT Pro Nav, Sunroof, 19" 403M, HUD, Rear Camera, DAB+, Comfort Access (20121250 Build, Delivered 25 January 2013)