Hubs of the Day are chosen from new HubPages writers' work. The following is from the HubPages FAQ:
"The Hub of the Day is an exemplary Hub chosen by the HubPages Staff to be featured on the signed-in homepage for one day and in the carousel of the signed-out homepage for ten days. Staff are looking for Hubs that contain interesting and useful subject matter, high-quality and grammatically correct writing, and beautiful formatting. A Hub of the Day accolade will be displayed on the Hub itself, as well as in the Hubber’s accolade box. To see previous Hubs of the Day, visit the archive. For more information on the Hub of the Day, check out our Blog post."
I wondered the same as you and had to look it up because I had Hub of the Day two days ago and I was very pleasantly surprised.