The primary problem with HF transmission while refueling is the possibility of coupling a significant amount of energy (enough to produce a spark across a small gap) in some nearby metallic object.
The aircraft, antenna, tanks and wiring may be in perfect shape. All failure modes of these subsystems may have been accounted for and designed to prevent inadvertent ignition of fuel vapors. But the situation on the ground is uncontrollable. There is no easy way to test every object that may be present within the near field of the HF antenna while on the ground for its ability to couple some radiated energy during a transmission. And since the area around fuel dispensing operations is classified as hazardous, eliminating possible ignition sources may require the prevention of introducing RF and/or electrical energy into them.