There is a principle reason that passenger airplanes look the way they do. The pressure vessel that they enclose the people within so that they might breathe. Easy to do with a tube, not so easy in a box. Huge difference in weight.
Other reasons equally as important to airlines..... People move around in an airliner. Flying wings do not like randomly changing CGs. People also are more comfortable sitting near a window. Very few windows beside passengers in a flying wing. Airports have very restricted ramp space between gates. Pulling a long tube full of people up to a gate is quite a lot easier than turning the tube sideways, sticking wingtips on the sideways tube and then taxiing it up to the gate.
There is way more to designing a passenger airplane than just choosing whatever aircraft layout/design suits your latest whim.