Nonprofit finance carries complexity that general CFO work doesn't prepare you for: fund-restricted accounting, grant compliance and release timing, indirect cost rates, donor-restricted endowments, audit and 990 obligations, and a board that is legally responsible for stewardship it can only evaluate through the financials it is given.
Most operating nonprofits cannot justify — and do not need — a full-time CFO. They do, however, need executive financial leadership: someone who sits beside the executive director, finance committee, and board treasurer; speaks the language of both the program team and the auditor; and brings sector judgment to the decisions mission integrity quietly depends on.