"1. Since your haven't provided the "good explanation" yet, we'll assume you haven't got a clue."
You make a lot of assumptions. A good explanation is the evolutionary one. The creature gained an advantage from these changes. We see a tremendous increase in the relative size of the mandibular foramen, far beyond anything required for blood supply or nerve function. This animal is storing fat all over its body as a food source, and insulation. Other functions for fat evolved such as the aid in locomotion provided by the specialized blubber of the dolphin. The body is going to put something in this void and fat seems to be the logical solution.
At the same time the foramen increases in relative size to the jaw, the ears are evolving rapidly also. All of these changes are occurring at the same time that whales are becoming obligate aquatic creatures never to return to the land. Any whale that has even a small advantage in hearing will be better suited to effectively survive and reproduce.