Wikipedia notes this about the VASIMR electric propulsion engine:
“Powerful superconducting electromagnets, employed to contain hot plasma, generate tesla-range magnetic fields. They can present problems with other on board devices.”
That’s a good reason to keep the engines as far away from people and equipment as possible. So the long engine hulls of the Enterprise are convenient because the VASIMR-like engines can be placed at the far aft end of them.
Once again, the form of the Really Big E offers a nice functional fit for building the world’s first supership in space.