To do what?
Guiding military troops and helicopters into a disaster area was not part of his job. It never was.
FEMA usually comes in after the cleanup has started, and takes names and writes checks. You need a bureaucrat to run this.
The hearing confirmation for his initial placement at FEMA can be found here. At the time, the Senate was under Democratic control.
Apparently, the complete lack of qualifications that are scathingly obvious to everyone now slipped completely past all these people, including Brown's legal troubles with the horse association, clearly delineated in the document.