Why are there no blended-wing passenger airplanes in operation?
All studies which so far showed an advantage for blended-wing bodies (BWB) were flawed.

The trick mostly used is to compare an existing airliner with a hypothetical BWB which uses equally hypothetical engines of improved efficiency, like what could be expected 20 years into the future. This masks the inefficiency of the BWB concept and makes the combination come out ahead.

The BWB will always have more surface area than a comparable conventional design. This translates into more friction drag and more skin mass, which more than offsets any advantage given by the bigger wing root (which helps to reduce wing spar mass). If you like real data, use the Avro Vulcan as an early BWB and compare it to its contemporaries. Note that design attempts for an airliner based on the Vulcan (type 722 Atlantic) went nowhere.

Why are these BWB studies published? The author gets more attention when he/she claims a "revolutionary breakthrough" than when he/she is more honest and admits that the concept is a dud. Even Boeing or Airbus like to publish BWB studies, so the public gets the impression they are ahead of the competition. It is sickening to read such academically dishonest studies - you need to spend time to dig to the bottom of the thing and to unravel the plot; however, once you have done this a few times, they all become alike. But compared to studies made 60 or 80 years ago, where the author factually lists what he did and why it didn't work out (which is the only way you can learn something), those modern studies are a waste of time.