Fauci is an infectious disease expert. If you ask him, his goal is to stop disease and that’s it. A political leader’s goal is to consider that alongside many other experts’ objectives, like economic well being.
If you ask a football center, his job is to block the nose tackle. If you ask a quarterback, his job is to position those blocks in a way that helps the team score. Trump is not discarding Fauci, he’s weighing his input against the other 9 players on the field.
Fauci tried to explain this concept in his full interview with CNN, who then edited the interview down to a very narrow view.