He's publicly said he stays because he loves the job itself and it's not about money. Harper's one of a handful of the current command who'd be genuinely qualified for Chief. The rest spent way too much time in non-law enforcement roles as Lts and Majors to qualify if the Mayor doesn't just want a repeat of Conrad's tenure here as Captain of the HMS Titanic. A couple others were or are Majors in inactive divisions, divisions where crime only went up, or running detective units with poor track recors