>> The only logical reason is that he doesn’t have one <<
It’s ONE logical reason to be sure.
But it’s not the ONLY logical reason.
For example, Axelrod and company may think that once the full BC is released, nut cases like Orly may go silent.
If such silence eventuates, then the Øbama team might fear that they wouldn’t have the continuing issue of “crazy birthers” to use against the Tea Partiers and/or the ‘Pub partiers.
True. It could be that, in the absence of his father, the actual birth certificate identifies his race as Caucasian (since neither "mulatto" -- nor even less so "African" -- is a racial classification).