The trouble with flying wings is the fuselage tends to be too short for carrying a lot of cargo. You can't put heavy cargo outboard in the wings because then it's tough to balance the load and the high rotational inertia makes roll control difficult.

Flying wings work fine for bombers because the "cargo" is very dense and will fit into a short bomb bay.

There have been proposals. Here's the Lockheed Spanloader concept.[1] Never built. The idea comes around again every once in a while.[2]

[1] https://books.google.com/books?id=jWlaIWwcsiwC&pg=PA112 [2] https://books.google.com/books?id=C0gUyoYewhoC&pg=PT183