Held to a higher standard of historical accuracy than other Oscar films

I would guess that's because some of that creative license involved the deaths of three innocent people. People tend to get sensitive about people being murdered, then a person convicted of the murders by a jury of their peers with plenty of evidence of their guilt in court, and then that person gets out of prison on some technicalities (not exonerated of the crime), because that's what really happened.

Furthermore, this film made Rubin Carter out to be this innocent person who was railroaded by law enforcement and the courts his whole life, when there were other people who spoke out after film was released who weren't murdered but were victims of his brutality, and give credible evidence of it. Read about Carolyn Kelley, his juvenile record or his prison disciplinary record. The movie makes no mention of any of this.

Other biopics have taken creative license as well, that's true but haven't usually involved a murder. Embellishing, exaggerating, twisting the truth somewhat almost always happen in movies "based on true stories" but this movie is such a bold-faced lie it should be considered pure fiction and nothing else.

Read the NY Times review of Ron Howard's A Beautiful Mind and you'll realize the film should have been titled A Beautiful Lie. The Oscar winning film received criticism for what it invented as well as for what it left out.