Why Kaga replaced Amagi after the earthquake

Why did Japan convert Kaga rather than another Amagi-class hull after the earthquake damaged Amagi?

Atago and Takao were less complete and had already progressed further toward dismantling, making Kaga the more practical replacement hull.

Carrier conversion depended on the physical state of available hulls, not simply on which design was theoretically preferable. Amagi's earthquake damage removed the intended battlecruiser conversion. The sister hulls Atago and Takao were not far enough advanced to offer the same shortcut and were already being broken up. Kaga therefore became the viable substitute despite originating as a battleship rather than an Amagi-class battlecruiser.