Max level Fighters get Extra Attack 3 which grants 4 attacks before spending their Bonus Action or a single resource. Add in things like Action Surge and some source of a Bonus Action attack (Polearm Master, Crossbow Expert, or even off hand weapon) and Fighters can easily get 9 Attacks.
Action surge is a part of it, but that is only usable once per short rest
So what's the rest of it?
Max level Fighters get Extra Attack 3 which grants 4 attacks before spending their Bonus Action or a single resource. Add in things like Action Surge and some source of a Bonus Action attack (Polearm Master, Crossbow Expert, or even off hand weapon) and Fighters can easily get 9 Attacks.
So, compared to Paladins and Rangers; action surge
Compared to Monks; nah lol