Cultural: The burial of the chief judge is accompanied by mourning and fasting. This may be a retention of tradition from the Old World, though it is not that unusual to associate abstinence from food with a time of mourning. In the Old Testament we find:
Esther 4:3
3 And in every province, whithersoever the king’s commandment and his decree came, there was great mourning among the Jews, and fasting, and weeping, and wailing; and many lay in sackcloth and ashes.
Even though Ester would not have been with the brass plates, the cultural practices referred to in Ester would have been present earlier. They are certainly a part of the Nephite tradition for burial:
Alma 30:2
2 Now their dead were not numbered because of the greatness of their numbers; neither were the dead of the Nephites numbered—but it came to pass after they had buried their dead, and also after the days of fasting, and mourning, and prayer, (and it was in the sixteenth year of the reign of the judges over the people of Nephi) there began to be continual peace throughout all the land.
Regardless of the ultimate source, there were specific signs of mourning that accompanied death, and one of the accompanying “signs” was fasting.