And before that Civil War, the Russians were doing all they could to suppress the Poles under their control, unlike AH control in nearby Galicia, where at that time after the 1860s, they were allowing local Polish administration.Most of the people there weren't even Polish, the Polish government took it from Russia during the Russian Civil War in a naked landgrab. Why should they leave?
Congress Poland, OTOH, was subject to intense Russification after revolts in 1830 and 1863
Despite the bans on education in Polish and emigration to Germany and USA, here were the demographics for 1897
Polish Jews 13.5%