The reason why only men attended, leaving out the women, was quite simple. It wasn't because of gender inequality leading to discrimination against women, but because the husband was the most crucial labor force in the family. Which woman wouldn't want her man to have a good meal to replenish his strength? Their household could barely manage to fill their stomachs throughout the year, let alone compare with the grand banquet's eight large bowls.
The five women present were either without a head of household man, or their men couldn't attend personally. They represented them, but the food they picked was piled into the bowls in front of them, and they couldn't bring themselves to eat it. They probably wanted to take it home for their elderlies and children to savor.
Although many old customs were abolished after the founding of the country, here, the Wanglou Brigade simply couldn't abandon its traditions.