Two protagonists, so two covers. Makes perfect sense.
During a reddit Q&A session, Assassin’s Creed Odyssey creative director Jonathan Dumont confirmed that physical versions of the game will have a reversible cover. One side with male protagonist Alexios, the other side with female protagonist Kassandra. You choose which side you want to display.
Source: Destructoid Assassin’s Creed Odyssey will have a reversible cover