0 Just a guess - all these items of clothing have two legs. That's why the plural. 0-
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00According to several costume historians who have helped me with this reply, the answer to all this conventional plurality is very simple. Before the days of modern tailoring, such garments, whether underwear or outerwear, were indeed made in two parts, one for each leg. The pieces were put on each leg separately and then wrapped and tied or belted at the waist
00So, partial answer - the clothing that covers the legs, bottom and genitals - was originally not in one piece and a pair of trousers was thus two leg-pieces joined together - with or without crotch cover. 12blockquote12br