Disney inherited from 20th Century Fox after their acquisition of 21st Century Fox.
When it comes to blockbuster films, and even Oscar-bait movies like Ford v Ferrari, studios tend to have different marketing strategies for different countries, and that extends to their titles, too. In recent years, there have been title changes for movies like Pirates of the Caribbean: Dead Men Tell No Tales (aka Pirates of the Caribbean: Salazar’s Revenge). Ironically, both of those films are from Disney, and now so is Mangold's Ford v Ferrari.
Fox hasn't given a specific reason for Ford v Ferrari's title change, and the studio likely won't do so since it's not necessarily something they would reveal to the public, but considering that the 24 Hours of Le Mans race takes place in and is an immensely popular European race, it makes sense to name the film after an event that Europeans - even those who aren't racing fans - would recognize on some level. So with that in mind, Le Mans '66 could be better than Ford v Ferrari, but certainly not from a creative standpoint.
Unless someone is well-versed in racing history, particularly with regards to European races, they may not know what Le Mans '66 is even about. On the surface, general audiences may believe that it's a racing film akin to Rush, when in reality, it's more about the development of the Ford GT40 car than it is about the race itself, despite both being distinct parts of the film. So altering the title to Le Mans '66 is, in some way, misrepresenting the story to audiences who may be expecting a straight racing movie instead of a drama.
Ford v Ferrari's European title downplays the core rivalry between the two companies in the early 1960s and the crux of what the film is about. Going from Ford v Ferrari to Le Mans '66 is like changing the title of Miracle on Ice to Winter Olympics 1980; that would cheapen the United States' hockey team's victory against the Soviet Union. It would've been a bad decision for that film, just like Ford v Ferrari's change is a bad decision.
