Far more likely to be mundane economic & legislative reasons determined by accountants such as packaging requirements (space for passengers), maintenance requirements (they need to fit in existing infrastructure hangars) and operational reasons such as getting the paying passengers on/off using existing terminals and airbridge infrastructure.
A radical departure away from the tube+two wings shape, around which the entire international airport infrastructure has been built would require an incalculable bill to replace it all. One that would last for decades during the transition period until all old tube+two wing aircraft had been retired from service. I doubt the costs could ever be recouped in anyone's lifetime. Hence, isn't worth doing.
