There are several layers to this, but I want to address some inaccuracies first:

This sounds very intuitive, until you realize that the US had - between Feb 1940 and Sep 1940 - put in orders for 11 Essex Class carriers with an aircraft capacity of as much as 1,100 planes. In the same time window only 5 Iowa class battleships were ordered.

The US ordered nine battleships in this period, four Iowas and five Montanas. Missouri and Wisconsin were ordered on 12 June 1940, the rest on 9 September 1940. Stephen Roberts has done an amazing job tabulating US Navy orders and reorders for the war, and in this case Friedman's US Battleships: An Illustrated Design History corroborates this information. I will reference both again.

It somehow feels like the US navy had a pretty good idea about the primacy of the aircraft carrier by September 1940, during which a particularly large order was split 3 battleships vs 8 carriers.

Actually the Two Ocean Navy Act authorized seven carriers (CV 13-19) and seven battleships (BB 65-71). To further this comparison, since 1933 the US had ordered 15 carriers and 17 battleships, and once the battleship building holiday ended the US ordered them in roughly equal numbers.

Before 1941, the US (and most other nations) were neither battleship nor carrier focused. Every admiral knew carriers had value in naval combat from the earliest days. The Washington Naval Treaty, signed in 1922, set building limits on only two types of warships: capital ships (battleships and battlecruisers lumped together) and aircraft carriers. But carriers filled a different role than battleships, and in the US Navy were mainly assigned to the Scouting Fleet rather than the Battle Fleet. They were complimentary systems, and this held even through 1944 War Instructions, where carriers played a critical supporting role while battleships filled the main battle line (see Chapter 12: Major Action for that).

With that in mind, go to Stephen Robert's FY 1942 page. The 5% Expansion Program (PDF) authorized two fleet carriers, CV-20 and CV-21. He does not include the next steps as they were conversions, not new orders: 24 escort carriers (Bogue class) converted from C-3 cargo ships and nine light carriers (Independence class) converted from light cruisers, all acquired and specific conversions authorized by 2 June 1942 at the latest (the last Independences) and most by March. At this same time, the US faced a major steel shortage due to the volume of new warships ordered: the sacrifices included suspending all five Montanas and launching Kentucky ASAP to clear the ways and steel for other ships (there is some evidence Illinois was also laid down and launched around this time, but I have not confirmed this). Eventually the Montanas were outright canceled, though construction of Kentucky and Illinois began again in late 1944 and the former continued until 1950. This shows a major shift from carriers and battleships to carriers over battleships (really carriers, destroyer escorts, landing craft, and a dozen other ship types over battleships, the explosion in US shipbuilding is very complex and I don't fully grasp all the ramifications).

Now to answer your question, who or what caused this focus? I'll start with the later shift first as this is clearest. Even before Pearl Harbor and the destruction of Force Z (arguably the more significant action, a modern battleship at sea sunk by aircraft was more significant that older battleships moored in a harbor) President Roosevelt was pushing the Navy to adopt small, austere carriers for more minor roles. The Navy was not willing to sacrifice as much capability as Roosevelt wanted, so the program advanced slowly, but even by mid-1941 a major CVE program was on the horizon and December 1941 was just the spark. Roosevelt in particular pushed for light carriers to supplement the larger fleet carriers as new ones were not projected until 1944 (we beat those projections) and CVEs after CVE-55 (the Casablanca and Commencement Bay classes), and while it was far easier after December 1941 he deserves much of the credit.

But before December 1941, in particular in 1940, thanks must go to another man: Congressman Carl Vinson. Vinson was a major Navy advocate in Congress and in particular pushed strongly for carriers throughout his years in office. His effect can best be felt by the other name for the Two Ocean Navy Act: the Fourth Vinson Act, and the Second and Third Vinson Acts authorized the first four Essexes and Hornet. If any one man deserves credit for ensuring these ships were built, it is Vinson, and for this reason the third Nimitz class carrier bears his name.