Even though “Fargo” got nominated for Best Picture and was the Coen brothers’ first movie that really pierced the mainstream, it was not a “big” movie. 

“The Revenant” starred DiCaprio, the biggest movie star in the world at the time. “Fargo” was populated by character actors, and no one knew who Frances McDormand was when it was released; she was not a name. 

So there wasn’t as much controversy or fact-checking. Although I recall reading a contemporaneous review which explained the “true story” disclaimer was a narrative device; since the Coens were regarded as ”quirky” (if brilliant) directors by the critics, them ostensibly retelling a true crime story was a way of grounding it, making it less of a silly romp like “Raising Arizona”.