They simply did not have the bombers available, and the British were not willing to share any of their orders.
Further, it was not just one "high placed spy", but the entire network. Chiang was not told, in 1942, about HALPRO, Force Aquila, and the Doolittle B-25s until days before they were supposed to be sent, out of fear the Japanese would find out and plan aerial counterattacks on where the bomber bases.
Chiang Kai Shek would probably be a bigger reason against bombing Japan...For all his bluster, he did not want to, because he knew what the Japanese response would be. He did not have his bombers carry bombs to Japan, only leaflets, despite the bombers ability to carry bombs. Despite the bombers leaflet success, no further effort was made to bomb Japan. On the "things to do" list of the AVG2, bombing Japan was low on the list at #5. Finally, we bombers were available, suddenly Chiang did not want the B-17s, B-24s & B-25s in China.
The bombers, had they been sent would not have been used to bomb Japan, but sent to bomb Japanese bases in China and to support China's ground effort. Which was Chiang's original intent.