The reason for their absence is because Meghan is throwing a party to celebrate their son Archie's 4th birthday, which coincidentally falls on the same day as the coronation.
While the rest of the world will be celebrating the coronation, Meghan will be hosting an intimate gathering of friends and family to commemorate her son's special day.
According to PEOPLE, Meghan's party for Archie will likely be a low-key affair, similar to past celebrations.
For example, Archie's first birthday was commemorated with a video to promote Save the Children's #SaveWithStories campaign, which aimed to help children impacted by the COVID-19 pandemic.
In contrast, Prince Louis, Archie's cousin, recently celebrated his fifth birthday with a pickleball set and an outdoor obstacle course.
As for what Archie will receive for his fourth birthday, the article's author speculates that he may receive a gift related to Roblox, a popular building blocks game for kids.
However, the author admits that they are not an expert on children's gifts and suggests that Archie may receive something from a curated list of gifts for 4-year-old boys.
In any case, Meghan's party for Archie is expected to be a private affair, as the couple has been known for their preference for privacy.