At the risk of starting a controversy, I will offer an answer. Since god sent me away from Paradise for giving his apple back to him, I rarely look at the other site. But, when I do, I see all of these new names that weren't there before. My suspicion is that these are folks who made a point during one of the meltdowns that they were leaving, but really just came back under another name.
So, if they don't have the balls to follow through and really leave, then I doubt they would register here. I think the posters that have made a success of posting on both sites, such as MsGuy, for one example, have made real contributions to both sites. It's people like him that we are lookin to attract, whether from the other site or brand new. There's is no reason you have to leave one to use the other, unless, of course that is your preference.