Why America converts only one Lexington hull

Why would the United States not sacrifice more Lexington-class hulls for aircraft carriers?

Carrier value was still theoretical in 1922, whereas the Lexingtons were already funded and matched the navy's established scouting doctrine.

The choice must be judged from the start of the treaty era rather than from later wartime experience. American officers knew how fast scouts were supposed to support the standard battle fleet. Carrier doctrine was still being tested, with Britain further along than the other powers. One conversion supplies an experimental aviation platform without abandoning most of a programme Congress had already paid for.