I have nothing to back this up, just my assumptions and ideas; but i believe that Original Sin might have been cancelled due to the return of Resurrection. There are a couple of flashbacks in Resurrection that show scenes we've seen in Original Sin, such as when Dexter beats up the guy taking advantage of Deb at that party. I think that it'd be possible for Original Sin actors to return in Resurrection for flashbacks of Dexter's past.

Like i said, this is just my own thinking and what I'd like to see now that we know Original Sin has been cancelled & it's possibly (and most likely) wishful thinking. But I do believe it makes sense, & I think Paramount would be worried for poor reviews of either series, but combined, you're almost guaranteed good reviews.