The risk of catching SARS-CoV-2 indoor is greater than outdoor, which I think many agree with. And poor ventilation and crowding make transmission much more likely, on top of other endless amount of factors like aerosols (from viral normal shedding) droplets (from coughing/sneezing), lifestyle stress (from work, poor nutrition, etc. that weakens the immune system, enabling viral replication and spread). I think all of these factors also make the infection and transmission rate highly variable among countries, or even among households.

Oh, and by writing that "Virus aerosols do not build up indoors," do you mean outdoors?