Called this morning and after some new info the reason is I don't have a long enough credit history. I did offer to close the United card and they said that it still shows a balance (I paid it last night but that didn't include a recent charge so there's still some change left on there) so I'll pay that off then she said I could call back and ask to close the United card and open the sapphire so I'm assuming that won't be a problem.