I figured out the main issue with fiora.
It is that most top lane mains enjoy playing tanky fighters and tanks, both of which stack hp and resists. Fiora is the champion that hard counters both of these classes. In addition to tanks having a rough time in lane vs fiora, they also get hard outscaled, leaving them with only the midgame. Most top lane mains are team players, and all "team player" champions are countered by fiora.