There is some pressure in this direction for respiratory illnesses. It's easiest to spread an illness when it's present in the upper airways (and thus easiest

There is some pressure in this direction for respiratory illnesses. It's easiest to spread an illness when it's present in the upper airways (and thus easiest to cough/sneeze out), but the illness does more damage to the lungs when it's deep in the tissues. If it were an exclusive choice, evolutionary pressure would tend to push the former, more transmissible route. The literature at least tentatively reports that Covid variants tend to make this shift (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10024278/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10024278/), which partially explains why the variants were more transmissible than Covid!Classic.