There isn't always some evil motive. They simply want to try expanding the game into some multiplayer aspects. They could, in theory, put in an offline mode I'm sure. But if the online component is significant enough they could feel that creating a crippled pure-offline mode that only a few die-hards will use would be a waste of resources.
That's my point. I don't assume they are doing this just to be dicks (although it's possible), I believe they think this is a good move. I just don't understand what their reasoning is that lead them to that belief. There wasn't - to my knowledge - a huge cry from people for the ability to play the game online. So unless they can demonstrate a real advantage to playing online (and some reason that you must play online), this seems to be a really bad decision.