because the UN will appoint someone like Goldstone to conduct them. But Obama is aware that the majority of the Americans know the truth about the terrorist act carried out by the Turkish jihadis with the help of the AKP, and aren't going to go along with demonizing Israel. Most of the Americans are already having second thoughts about Obama and he can't afford to keep alienating more people by unfairly singling Israel out.
Three Afula residents arrested in right-wing protest (Haaretz)
from the article: 'Obama warns Erdogan international Gaza flotilla probe bad for Turkey'