The reason the ULL is forecast to have less of an effect is because it is cutoff from the jet stream and lacks any real extending fronts/trofs. Because of that the ULL isn't creating a path to the westerlies that the hurricane can follow. So instead of recurving it, it will only nudge it north. Also, because most of the energy is in the upper levels, the ULL can cause shear since the upper level winds are strong cyclonically, but the surface winds are mostly easterly. And the intensity of the low is also important. A weak ULL is less likely to have a surface/mid-level reflection(low pressure at the surface/mid-layer as well as the upper levels) and less of an impact on storm motion.

However, an important factor is that ULL's don't really recurve storms. Storms recurve due to fronts/troughs associated with extra-tropical storms. The main difference is that extra-tropical storms usually have low pressure centers from the upper levels to the surface and are embedded in the jet stream. Cutoff lows like the one in the Bahamas don't influence tracks as much as they can create shear.