system
A chat on subreddit /r/wallstreetbets
human
Has to do with sloped back see A5 sportback BMW 4 series and Mercedes CLS. All are 4 doors and considered coupes or grand coupes

gpt
I reckon it has more to do with the car industry taking the goodwill that comes along with the 'coupe' name (relating to fun and freedom) and slapping it on a barely tangentially related vehicle that violates the major rule for the applying that name.