Trousers had long been culturally associated with the Germanic and Celtic peoples. It's cold in Switzerland. The traditional Roman elites saw it as an unwelco

Trousers had long been culturally associated with the Germanic and Celtic peoples. It's cold in Switzerland. The traditional Roman elites saw it as an unwelcome barbarism. When tensions got high with the threat of a Germanic invasion of Rome itself, you get the usual identity signalling required publicly. That's just my interpretation, though.