Control and money. Also it doesn't seem baseless to consider the publishers history when they make current decisions. This way they can also try to stop those cdkey sale sites that have been cropping up and hitting Origin which only has regional restrictions on its actual storefront.
Same story as Diablo 3, protecting their online crap (DLC storefront) from piracy/cheating. That's the excuse anyway.
I don't buy it. EA has had much bigger games come out (and planning to come out) that have no hint of an "always on" connection requirement. SimCity is not a big enough franchise that they can count on previous purchasers to buy it regardless. They must have had some reason in mind for an always online requirement (assuming the news is accurate, so far the sites reporting it are the types to report every rumour they come across) beyond simply DRM.