As much as the Soviet Union tried to keep down Jews, they were also trying to promote people who fit a nationalist narrative. So it wasn't just antisemitism, it was also affirmative action for Russians (especially those of peasant descent).
I took Yiddish in university for a while. During the soviet years they tried to neutralize any hebraic or biblical references. For example, in hebrew the word for friend is "Chaver". It's the same in yiddish. But the soviets insisted that it be changed to the more germanic "fraynd". Similiarly, they insisted even on the changing of spellings to make the language altogether less hebraic and jewish - and more neutralized and soviet.