Why American ships of the line were awkward Royal Navy reserves

Would the Royal Navy have used American ships of the line as a reserve fleet as it did captured French ships?

Only opportunistically if they were captured; American ships were less compatible with the Royal Navy's worldwide service requirements than French or Spanish prizes.

The Royal Navy might have commissioned an American ship of the line if it captured one, but no such reserve fleet materialized. French and Spanish prizes fitted British needs more naturally because all three navies expected major warships to serve around overseas possessions. The American ships emphasized rapid construction, very heavy armament, and comparatively short service lives. They could keep the sea in bad weather, yet were less suited to the sustained global station work expected of British capital ships. Compatibility with operating doctrine and logistics therefore mattered as much as the number of guns aboard a captured hull.