Though it does not adapt one specific event or tragedy that has occurred in American history, the film is still an r-rated take on American special forces, and elsewhere in my interview with Mark Wahlberg he explained that it was important for the team behind the film to nail that intensity to honor the type of story they were telling.
Of course, it’s worth noting that Mile 22 is still a pretty intense movie, regardless of whether or not it’s fictional.
This may have been a more fun film for them to make, but it simply could not be done with a PG-13 label.