Why a Spanish cruiser hull did not make a good light carrier

Was cost the only reason Spain abandoned a postwar plan to convert a cruiser hull into a light aircraft carrier?

No; the hull was considered adequate for a cruiser but poorly suited to the carrier role.

A hull that works as a cruiser may still be unsuitable for an aircraft carrier. The postwar Spanish conversion proposal failed on suitability as well as cost. The brief answer does not specify every structural defect, so it cannot support a complete reconstruction of the project. A large existing hull is not automatically a sound foundation for a flight deck and aviation spaces.