The point was made early in the thread by Brian about focusing on getting rid of sub prime products overall. I know in my own experience, as well as seeing it with others, Cap1 can be strange sometimes when it comes to upgrading or in this case, making your account unsecured.
They have this reasoning of an internal way of deciding who and when for these things, and if you look at various data points from others who have or haven't been successful, it doesn't make sense a lot of times. And by talking to them, they give you the idea that it is a computed decision and that they can't manually evaluate the situation. For me personally, this was a reason I dropped them. But like I said, others have had great experiences with them, or never had these hassles.