The long hair was the insidious effect of California culture, and an unfortunate departure for Eddie.
The crew cut is the perfect complement to his obsessive mindset when he is at his best, top of his game. A very militant look.
In the movie, he may have a relaxed "business cut" as a reporter. Following symbiosis, I envision a scene where Brock is shown with a new buzz-cut during a punishing workout, to signify his newly obsessive mindset.