Peacetime Cerberus versus Civil War emergency monitors

Why did the United States not turn its Civil War monitors into a durable Cerberus-style coastal fleet?

The Civil War ships were emergency builds optimized for immediate service, unlike the deliberate peacetime investment behind Cerberus.

The obstacle was what the United States was trying to buy. Cerberus was designed in peacetime by governments able to spend time and money on a deliberate solution to anticipated threats. American Civil War monitors were emergency vessels needed for immediate service, so rapid construction outweighed a long service life. Wooden hulls and other compromises followed from that urgency rather than from an inability to imagine a more durable ship. Emergency programmes may consider a decade of use if fortunate, but rarely optimize vessels for service several decades later.