In the same article, these are “children” (15-17 year olds) tried as adults for serious crimes such as murder.
The problem is that this makes rehabilitation more difficult which in turn leads to recidive.
Back in the 90s (when I looked into this cause it was part of political standpoints by politicians in my country) both the general public and behavioural science was on the fence whether longer punishments or shorter punishments with a focus on rehabilitation worked better. A quick search on DDG showed news articles and studies arguing both ways.
Which is why they aren't the ones who decide sentencing.