This is why they hold the leadership vote just days after the November election, before the new members are sworn in.
They tell the winners that they can vote in the leadership vote, but they pressure them as rookies to fall in line and just vote for whom they tell them to.
In 2020, Democrats held their party leadership vote on November 18 and 19. I can't find any articles that include the dates for the Republican leaderships votes, but they are in November, too.
-PJ