I think they put the hannahs suicide scene in the first place bcs they want to show hannahs pain, how depressed she was and how hurting she was inside that she cant feel anything anymore, then decided to hurt herself physically and end her life to stop all the pain she felt..
Maybe they want to show the pain so that the ppl who watched it could realize what some ppl have gone through..
*sorry if it confusing im not really good with words :(