I have no idea, this is just a guess.. the only reason I can suspect IF it was an honorable intention (that is a BIG IF) was that he was protecting the privacy act of 74 by not creating a precedent. I know, big stretch assuming there where honorable intentions...
In reality, IF it was legit Hawaii birth, maybe it showed his parent’s weren’t married? Didn’t want bastard jokes?
All wild guesses.
his dad was already married, so BO was in effect a “b”.
marriage wasn’t legal.