Why use sloops instead of shallow-draft Fly-class gunboats?

Why were sloops used as gunboats when the Fly class had shallower draft and better handling in confined waters?

Because Fly-class vessels were valuable merchant conversions and were sold off quickly, while sloops attracted less favorable sale prices and remained available.

This exchange shows that postwar fleet composition was shaped by disposal economics as well as tactical suitability. The Fly class could fetch good prices for commercial service, so the Royal Navy did not simply retain every vessel best suited to shallow rivers. The remaining sloops then absorbed gunboat duties despite their less specialized hull form.