What reasons did the Supreme Court give for changing lifetime sentences to youths?

The Court argued that these special groups of offenders are less guilty than those of adult offenders with no intellectual disabilities who have committed the same crimes. The execution of people who were under 18 at the time of their crimes violates the federal constitutional guarantee against cruel and unusual punishments.

Intellectual disabilities of youths compared to adults

meting out of unjust punishment

Explanation:

The supreme court changed the lifetime sentences been passed to youths (under 18) for crimes committed as well by an older person because the court sought to address the narrative that younger people tend to have more intellectual disabilities compared to matured/older persons in the society.

meting out the exact same punishment on both young and older offender will be contravening the laws in the constitution that goes against serving unjust punishments for crimes committed.

giving a life time sentence to an offender lower than the official age of adulthood would be seen as an unfair sentence.