It's a simple and easy way to reduce chances of spreading it to another person. It diverts airflow from directly forward, changing the distance outward that aerosols from your mouth go. Since, as you point out, this virus is spread via aerosols, this impacts the chances of spreading it, by reducing the contagion radius around you.

Simple and easy and, given the miniscule risks to all but the unvaccinated, completely unreasonable to impose on others.