@jonathaneze Paisen did it as a revenge against his dad, as a form of rebellion to show him that he was not trash like him and that he could be his own man, and seeing how much money he forced him to spend it kind of worked out, plus he took his brother down, Paisen never felt guilty about the accident, on his mind it was just that, an accident, what troubled him most was not being loved by his dad or anyone else.
The others did it out of guilt, they wanted to atone by confessing and doing time since atoning on their own way didn't seem to work, except for Maru, he was feeling lonely and just went with the flow just to not be left behind, but he never felt guilty, he genuinely believes that those delinquents had it coming.