I don't buy that they don't have another reason. I don't believe that EA decided to make an online DRM experiment with a game like SimCity. I believe that they had something else in mind - it's just a matter of what that "something" is. Could be the social element that has been mentioned, that's plausible.
Anything with Sim in the name is likely to sell decently and EA needs exclusive properties to fuel the Origin vehicle.
I don't really agree. There's a large market for The Sims, but that doesn't mean anything with "Sim" in it will sell. The fact the rest of the Sim franchise has been effectively dead for so long demonstrates that. If they were really interested in pushing Origin, they'd focus on getting as many sales as possible, rather than extensively burdening the game with more restrictions.
I guess there's nothing to do but what and see what they announce. As I've said, I'm still skeptical about this "announcement" in general - we've only seen 2nd-hand reports.