He creates an aerosol cloud that lingers on the path, that could be inhaled by someone further behind. It doesn't have to be a wheel-sucker.
I'm sure you have experienced riding into someone's cloud of exhaled tobacco smoke, or perfume or cologne. If you can smell that, you are probably also inhaling virus particles if they are being shed.
The objection based purely on etiquette should be compelling. The public health concerns simply make this more emphatic.