The initial purpose of the banquet was to introduce Lily as a part of the royal family. However, since Princess Mikaela had sent the invitations before Lily could refuse, they had to make it look like this was another banquet meant to celebrate an achievement they recently achieved.
Another issue came up when Lily got exhausted due to her long trip. This valid reason made Mikaela and the Duchess reschedule the banquet. Of course, this was never a problem for noble families. This was mainly because the actual goal of these nobles was to interact with the other businessmen and important individuals from the neighboring countries of Luxembourg.
Business — that was the primary goal of attending these events.
They wanted to broaden their influence and take advantage of Luxembourg's open economy. Business and Influence. Wasn't that what everyone wanted? Unfortunately, Harringfort was not here for the same reason.