Recently I stumbled upon this paper from a few years back, The invention of trousers and its likely affiliation with horseback riding and mobility: A case study of late 2nd millennium BC finds from Turfan in eastern Central Asia. Basically, it seems that trousers emerge with mounted cavalry. The dominance of mounted cavalry in the years after the fall of Rome resulted in the emergence of a trousered elite, and the shift away from the tunics of antiquity.
Today we don’t ride horses, so the utility of trousers in that context is gone. It seems that if you work in blue-collar professions and it cold climates trousers are still useful. But is there a reason for men in warm climates in white-collar professions to continue going with trousers as opposed to a simple tunic? Are we just stuck with tradition?