Why do we say a “pair of pants” when there's only one of them

First pants worn by horse riders 3,000 years ago

Yogipace,4 Pockets/Belt Loops,Extra Tall Women's

Watch Riveted: The History of Jeans

3 Ways to Hem a Pair of Pants - wikiHow

Ask Uncle John Anything: Why Is “Pants” Plural? - Portable Press

Why is 'pants' plural but not 'shirt'? - Quora

3 Ways to Hem a Pair of Pants - wikiHow

Usage and etymology of a pair of - English Language & Usage

Why is underwear plural when it's only one? - Quora

I've ripped my pants and been laid off, they don't feel similar at