Because after all of our efforts by all of our best minds, since the first recorded outbreak of bubonic plague 2000 years go, nobody has found a way to cure a viral infection.
But we certainly know how to develop vaccines to prevent viral infections.
That's why only fraudsters like Diwan, without any education or training in virology, and no track record of accomplishing anything in his entire life, claim to have found a "cure for the near totality of all lethal viral infections".