I suspect it has much to do with people being slow to accept big changes in some systems. Boeing (and surely other airplane manufacturers) has investigated and

I suspect it has much to do with people being slow to accept big changes in some systems. Boeing (and surely other airplane manufacturers) has investigated and considered lifting body designs - https://en.wikipedia.org/wiki/Blended_wing_body https://en.wikipedia.org/wiki/Blended_wing_body - but chose to move forward with traditional designs. I don't see the news item now, but I read that Boeing felt it was just too radical for passengers to accept (despite the significant advantages). It will probably take some wealthy "renegade" type to start a new airplane company that offers new designs like this.