Rx sales are significantly tied to sales forces as a physician has to write a prescription to drive revenue. If they don't, you don't make any revenue.
Advil and Tylenol have had large Rx sales forces for years.
The reason small biotechs don't have blockbusters is they don't have big sales forces. Partnering with BP gives them a big sales force and much large revenue potential. Cytodyn only has Vyera and a 13 person sales force and is the most hated company in HIV. Right now they support a $50 million drug.