"I didn't want to. There was no reason for me to," Gooding Jr. told PEOPLE during the FX Winter TCA Press Tour on Saturday in Pasadena, California.
"If I was playing him today, I'd have to put on a lot of weight," said Gooding Jr., who portrays the former NFL star during his 1994-95 trial for the alleged murder of his ex-wife Nicole Brown Simpson and her friend Ron Goldman.
"I know what incarceration does to a man. I have friends and family who have been incarcerated. They click and they start to believe whatever it is that they believe as the real thing that happened to them."
Gooding Jr., 48, adds he "didn't want that in this performance.
"He wasn't that. He was this flamboyant, charismatic, movie star, marquee-athlete. I needed that arrogance. That was where my focus was."
American Crime Story: The People v. O.J. Simpson premieres Feb. 2 at 10 p.m. (ET) on FX.
Reporting by CHRISTINA DUGAN