Why was a defendant in his 20s who attempted indiscriminate murder reduced his sentence by three years on appeal? (South Korea)

A defendant in his 20s who brandished a weapon at a passerby he did not know received a reduced sentence on appeal. The appeals court found that the defendant attempted to kill someone but then took rescue measures, and that he committed the crime in a mentally unstable state.
According to the Korean legal community on the 29th, the Suwon High Court overturned the original ruling and sentenced Defendant A, who was sentenced to 15 years in prison in the first trial for attempted murder, assault, and other charges, to 12 years in prison.
The court also ordered that the defendant be placed under medical supervision and wear an electronic location tracking device for 12 years. The appeals court said, "The defendant committed attempted murder, assault, etc. on a victim he did not know without any particular reason.
The court ruled that "the victim of the indiscriminate crime and attempted murder is likely to continue to suffer physical and mental aftereffects and pain for a considerable period of time," and that "he has not received forgiveness from the victim."
However, "the fact that he provided medical assistance after the attempted murder, fully admitted to the crime and showed remorse, and that he committed the crime while his ability to discern things and make decisions was weak, etc.,
Considering the various sentencing conditions, the sentence imposed by the original court seems somewhat heavy and unjust. Defendant A was found to be using a mobile phone while walking along a promenade in Yongin City at around 7 p.m. on April 10, 2023.
He was indicted on suspicion of stabbing Mr. B (in his 20s) with a deadly weapon without any particular reason as he was walking while looking at a movie, assaulting him several times in the face and body, and attempting to inflict injury on him.
Mr. B suffered serious injuries that required 16 weeks of treatment to heal, and received treatment at a hospital.
On the early morning of the day of the crime, defendant A kicked the head of a man in his 30s, C, whom he did not know, on a road in Icheon City, causing injury.
He was arrested on the spot for strangling Mr. D (in his 20s) who tried to stop him. After being questioned by the police and returning home, he was investigated and was found to have committed the crime again.
The first trial court ruled that "the defendant committed indiscriminate crimes against victims he did not know without any particular reason, and even if the murder attempt was unsuccessful, it is a murder that violates human life.
The court sentenced Defendant A to 15 years in prison, stating that "crime against humanity is a serious crime that cannot be tolerated for any reason."