Strange game launch (Far Cry 3)

The guys bought the deluxe edition through EGS asked to go through the yubisoft laucher, did it, but the initialization error or the connection to the server refused to start. I closed EGS, launched it through pure Uplay, it requested an account on Steam and after that it started, What's the catch? This is a Yubesoft game, why does she need a Steam account? There is no ban anywhere