Why expanded treaty fleets push Italy toward carriers

Would Italy build carriers under the earlier, more generous Washington treaty counterfactual?

Probably, because larger British and French carrier programs would make an Italian fleet carrier politically and strategically difficult to avoid.

Italy could continue using seaplane carriers for some light aviation tasks and did not naturally favor large fleet carriers. The calculation changes when Britain fields many more carriers and France builds to avoid falling behind. Mussolini's regime would be unlikely to accept a conspicuous French aviation advantage. Competitive prestige and Mediterranean balance would therefore push Italy toward at least one fleet carrier. Completing the Francesco Caracciolo ships is also expected to make an Italian carrier programme more likely.