HIV has a crazy high mutation rate, way larger than other viruses like SARS-COV-2 or the influenza virus. In an infected untreated human, you have at least one

HIV has a crazy high mutation rate, way larger than other viruses like SARS-COV-2 or the influenza virus. In an infected untreated human, you have at least one copy of the HIV virus produced for each base pair mutation within a day or so. In other words, if there is a single base pair mutation that makes HIV resistant to a single drug, HIV will adapt quickly. So that's why they quickly discovered to do double therapy, and nowadays one does triple therapy even, so that a virus has to randomly become resistant to three drugs at the same time.