Because he can’t.
The President has presented himself as Barack H. Obama. He served as Senator under that name. He ran for president and won under that identity. Keep something in mind, here, the information (if true)that he was adopted by Soetoro did NOT come from Obama. His biographies do not say that, best as I recollect. This is something that has been uncovered by the “birthers” such as it were. We’re waiting for confirmation of that fact. I suspect Abercrombie has learned it himself. This makes perfect sense, once you think about it: Abercrombie has indeed found a birth record (that could be Hawaii, Kenya, Boston, or Tulsa) that mentions Barack Obama. But he cannot locate a birth certificate reflecting that name, if Obama was later adopted, since that is the name reflected on the updated birth certificate.
What someone needs to ask the good Governor is if he has a Hawaiian BC under the name of Barry Soetoro. Then you have the Gov in the crosshairs.
That would require a free, independent press. Which is why I'm holding out for divine intervention.