Preparing civilian trawlers in peacetime carried a naval budget cost

Why did Britain not require all prewar trawlers to be built to military standards?

The Admiralty would have had to pay the industry-wide extra cost from its own limited budget, so it built some naval trawlers and relied on rapid wartime conversion instead.

The government could require or encourage military features in commercial trawlers only by paying for them. That money would come from the Admiralty budget and could grow into a large continuing subsidy across the fishing fleet. The Navy built a smaller number of its own trawlers with naval crews and accepted that civilian types could be converted quickly once war approached. Officials understood their value but chose when to spend scarce peacetime funds. The decision balanced numerous simple mobilization assets against complex warships with long construction times.