it would have gave the movie authenticity - a

no re-enactment would fully capture the actual fighting - b

and because we've all seen the BS Rocky movies - c

people who don't know Micky Ward's fights, post 104, were probably like yeah right

the fight footage would have put the movie over the top IMO

and they interview Micky at the end of the movie with his brother, so it's not like people aren't able to connect the character and the real person within the context of the movie anyway