Perhaps because that is the real test, that is the father's nationality. What some other country considers a person to be is of no importance. It's the parent's citizenship when the child is born, not the child's "dual" citizenship, if any. Even if the parent's country doesn't consider the child one of it's nationals, the child may not be a natural born citizen.
This appears to me to be a deliberate attempt to call Obama’s eligibility into question even if discovery were to show that either there was no legal marriage recorded in HI or the marriage was bigamous.
However, absent a legal marriage between Obama’s parents, Stanley Ann was a single US citizen mom and the 1948 BNA would not have made Obama a dual citizen. No foreign sovereign would have any claim over Obama, as the founders stated to be their concern at the time of the drafting the natural born citizen language.