I didn't realize the significance of the date. Anyway, the characters featured in those chapters had more important things to deal with at the time.
And the crew that we saw commemorating "First Contact Day" was the crew of Voyager, mainly through Neelix's initiative, which was the sort of thing you'd expect of a morale officer. It doesn't really reveal much about the scope of First Contact Day celebrations overall.
In fact, given as how Earth has, as of April 2163, only recently emerged from being a Vulcan vassal state, it makes a certain amount of sense to speculate that maybe First Contact isn't quite as revered a historical event for Humans of the 22nd Century as it is by the 23rd or 24th.
I don't know about that. First Contact meant more to humanity than simply opening the stars to them; it meant an end to war, disease and famine on Earth, and brought humanity closer together than anything ever had before. If anything that event should be more
significant to the humans of 2163 than those who came later; there still would have been people alive then who actually witnessed Earth in its post-World War III state and experienced firsthand the changes first contact with the Vulcans brought.
I imagine the anniversary of the founding of the Federation holds more weight with humans of the 23rd or 24th centuries than the anniversary of first contact.