According to his defense attorney, Ethan Couch suffered from Affluenza, therefore he shouldn't be punished because he didn't understand that he did anything wrong.

Sources:

True Crime Story: Smugshot: Affluenza

Ethan Couch - Wikipedia

What Happened to Affluenza Teen Ethan Couch? DUI Case Timeline (expresslegalfunding.com)

Tarrant crash victim: 'Momma, I love you. Please hurry!' | wfaa.comBurleson pastor's son speaks out about accident that killed four | khou.com

Tonya Couch appeals charges again in 'affluenza' teen case | wfaa.com

'Affluenza' Dad, Fred Couch, Arrested for Family Violence - D MagazineEthan Couch “Affluenza” Judge Jean Boyd No Longer A Judge (2paragraphs.com)Ethan Couch 'affluenza': 10 years since drunk-driving crash | wfaa.com

'Affluenza' DUI Case: What Happened Night of the Accident That Left 4 People Dead - ABC News (go.com)Ethan Couch, The 'Affluenza Teen' Who Killed 4 People While Driving Drunk (allthatsinteresting.com)