Consider this: there's no way the US could make an agreement to give/sell the uranium directly to Israel.
They could however arrange a way for Israel to acquire the uranium, which, if discovered, would place the blame on Israel rather than the US.
They could also take steps to prevent any investigation into that transfer.
There is precedent for this kind of illicit trade, so it's not entirely unlikely that the reason nobody looked into it too deeply is because it was meant to be stolen, and the US likely got something in return for the exchange that was worth maintaining the cover for.
They could however arrange a way for Israel to acquire the uranium, which, if discovered, would place the blame on Israel rather than the US.
They could also take steps to prevent any investigation into that transfer.
There is precedent for this kind of illicit trade, so it's not entirely unlikely that the reason nobody looked into it too deeply is because it was meant to be stolen, and the US likely got something in return for the exchange that was worth maintaining the cover for.