Neut, you’ve overlooked a more important reason why the white shirt/ black pants is a relative recent adoption.
Prewar Europe had no social net and one had to work to eat. Shtetl Jews were peddlers, bakers, tradesmen and manual laborers. White shirts and black dress slacks were not appropriate. However, now that non professional labor has so fallen out of favor, the mode of dress has shifted.
Joseph, in what specific way did weekday work clothes of the average Polish or Russian Jew differ from their gentile neighbors?