It's for people with strict nat. But you are connected to their servers at all times.
My baby is right on this.
That's something I don't understand. If the developer adds a solo option to the game why make the person still be online? Just make the solo portion be offline and keep the online and offline stuff separate.
Because what you don't get is this is not a single-player game It is 100% multiplayer, the solo is there because of things that are in the game, which can make it easier for you. Also if you don't wanna play with someone else at that time.