The phrasing here is a little confusing, but it seems like you're trying to ask the simple question of "Why was the Pacific Fleet moored at Pearl Harbor instead of on the West Coast on December 7, 1941?" If you're trying to ask another question, please let me know and I'll see if I can answer it.

The Pacific Fleet was moved to Pearl Harbor in spring 1940 because President Franklin Delano Roosevelt ordered it there. The U.S. Navy conducted large-scale annual exercises throughout the 1920s and 1930s called "Fleet Problems" that usually involved dozens of warships and thousands of men. Fleet Problem XXI in April and May of 1940 was conducted in waters around Hawaii. When it concluded in early May, Roosevelt ordered most of the fleet to remain at Pearl Harbor. I have never seen a detailed account of the decision that led to this, but most sources attribute it to a decision made with the support of the State Department. The general thinking was that moving the fleet would have a deterrent effect on Japanese expansion and signal that the United States was prepared to defend its interests in the Pacific.

The decision was made against the advise of his military commanders, however. Admiral James Richardson had recently been appointed Commander in Chief of the United States Fleet (CINCUS) in early 1940 and disliked the move to Pearl Harbor. Richardson felt that the Navy was unprepared to go on the offensive in the Pacific at the time, and the facilities at Pearl Harbor were inadequate anyway. Placing the fleet at Pearl Harbor did not improve its military readiness and did place it in a more vulnerable position. He would have preferred it return to its bases on the West Coast, including San Pedro and San Diego. Richardson asked his superior, Chief of Naval Operations (CNO) Harold Stark about the decision to place the fleet at Pearl Harbor, and Stark told Richardson that the fleet in Hawaii was believed to have a deterrent effect on Japan. Richardson raised the issue again in September 1940 with the civilian Secretary of the Navy, Frank Knox. Still dissatisfied, he brought it up in October 1940 with President Roosevelt during a trip to Washington, D.C. The President rebuffed the Admiral once again. Richardson responded with the following statement:

"Mr. President, I feel that I must tell you that the senior officers of the Navy do not have the trust and confidence in the civilian leadership of this country that is essential for the successful prosecution of a war in the Pacific."

That is jarring at best and perhaps even bordering on insubordinate. Roosevelt took the comment politely and Richardson left. But in early 1941, Roosevelt signed an order reorganizing the command structure of the fleet, and Richardson was removed from command. His replacement was Admiral Husband Kimmel, who was in command on December 7.

The diplomatic situation between the United States and Japan continued to devolve after the fleet was moved to Pearl Harbor in May 1940. Japan moved into northern Indochina in September 1940, and signed the Tripartite Pact with Germany and Italy that same month. Negotiations between the US and Japan made little progress in 1940 and 1941, and the US continued to supply Chinese forces who had been fighting against Japan. Japan occupied the rest of Indochina in July of 1941, putting airbases within reach of the Philippines, Malaysia, and Singapore. By that time, Japan was moving closer and closer to the final decision to go to war in the Pacific, and was beginning to focus on the idea of an attack on Pearl Harbor to commence hostilities against the United States.

While the United States had cracked the Japanese diplomatic codes (which you refer to), military plans for the Japanese were not discussed in these messages. There was no need to do so. It wouldn't have been necessary for the Japanese to inform their diplomats on the military picture, so they didn't. The Japanese diplomats continued on in their negotiations and were unaware of the attack on Pearl Harbor until December 7.