Why civilian carrier conversions wait for a major war

Why do smaller navies not plan civilian ships for conversion, given VSTOL aircraft and modular systems?

They tend to consider civilian conversions only when a major war creates an urgent need.

VSTOL aircraft and modular systems invite the suggestion that smaller navies should plan civilian ships for wartime conversion. The response agrees with the possibility but identifies a recurring delay: serious interest in converting civilian ships tends to begin only after a major war has started. Peacetime planning would have to anticipate a demand that governments otherwise treat as an emergency requirement.