The IJN ordered 4 Amagi class battlecruisers (Amagi, Akagi, Atago, and Takao) and 2 Tosa class Battleships (Tosa and Kaga) to form the "Eight-Eight Fleet". All ships started construction between 1920-21, but were terminated by the Washington Naval Treaty. All 6 unfinished warships had to be scrapped.
As the treaty allowed each signatory to use two existing capital ship hulls for aircraft carriers, with a displacement limit of 33,000 tons each. Japan initially chose Amagi and Akagi. However the hull of Amagi was heavily damaged due to Great Kantō earthquake, the hull of Kaga was chosen to be converted as Aircraft Carrier.
Why didn't the Japanese Navy choose the hull of Atago/Takao, and select the slower Kaga to replace Amagi as an aircraft carrier?