Interesting question. Could it be because she had named Obama Sr as the father in the fantasy divorce, used a kenyan birth certificate to enroll the boy in kindergarten and Frank Marshall Davis, Neil Abercrombie, Obama Sr and Pake Zane (and probably Stanley Armour Dunham) were all going to be at the reunion?
I can't think of a better time to introduce the boy to his fantasy father. Besides, how would you stop the boy from finding out his 'father' had been to visit in Honolulu and didn't take the time to see his 'son'?
"Barack Hussein Obama Sr’s trip to Honolulu in Dec 1971 was bracketed by two trips that Obama's old snack bar friends from the University of Hawaii made to see him in Kenya. Late in 1968, Neil Abercrombie and Pake Zane traveled through Nairobi on a year-long backpacking trip around the world and stayed with Obama for several days before they made their way on to the port city of Mombasa and to India. No mention was made of Stanley “Ann” Dunham or Barack Hussein Obama Jr. Neil Abercrombie is now Hawaii State’s 1st district Representative in the US Congress. He is a member of the Congressional Progressive Caucus who until 1999, worked in open partnership with Democratic Socialists of America. Pake Zane runs a store called Antique Alley in Hawaii. Although in the 1960’s Hawaii offered a diverse cultural mix, native Hawaiian Pake Zane recalls that “He (Obama Sr.) was the first real black man I ever met”.
images at link
The sad truth for Barack Hussein Obama Jr, is that Obama Sr didn’t return to Hawaii in December 1971 to see his son, but rather to go party with his friends Neil and Pake. That is why there aren’t any pictures of Obama Jr. with his dad as an infant, nor are there any pictures of the Dunham grandparents and Obama Sr. Sadly the only picture from when Obama Jr’s dad returned to Hawaii is at the airport while Obama Sr. waited for his luggage.
and this one - an undated image found later.