This is because the virus is actually inside the cells of the throat, deep in the tissue. Bacteria only infect around the cells. Because of this antiseptic throat lozenges, brandy etc kill the bacteria when they come into contact with the bacteria.
Antiseptic throat lozenges have no effect at all on killing viruses.
Bacterial sore throats respond very well to antibiotics but won't work with viral sore throats.
Bacterial sore throats rarely cause nasal congestion either.
Ok bacterial sore throats can be more painful but they are far easier to treat and heal quickly.