Reading more about this at one of the universities that participated in these studies, I should have called this a "cough cloud simulation" If I am reading it right, the reason these clouds go farther and stay in the air longer is explained as follows.
The researchers of the consortium modelled the airborne movement of aerosol particles smaller than 20 micrometres. For a dry cough, which is a typical symptom of the current coronavirus, the particle size is typically less than 15 micrometres. Extremely small particles of this size do not sink on the floor, but instead, move along in the air currents or remain floating in the same place. Studies of influenza A have confirmed that the influenza A virus can be found in the smallest particles, which measure less than 5 micrometres.
Researchers modelling the spread of the coronavirus emphasise the importance of avoiding busy indoor spaces | Aalto University
This is probably why Dr Birx recently warned us to stay out of grocery stores etc as much as possible. I haven't set foot inside anywhere except my own home for 3 weeks. If I had to I would wear a mask.