Because it only got two stars in its Euro NCAP crash testing.
Ford didn’t expect the car to be tested and therefore didn’t fit various safety items as standard. Which I suppose makes sense. If your car isn’t going to be tested why bother? Nobody will ever know.
Sniff Petrol have another version of events which sounds perfectly plausible.
I can see the tweet from the Great Leader:
“Mustang only failed because tests too hard. SAD. 50% tariff on all European built cars from tomorrow.”