Democratic unity has always been a notoriously difficult problem for the larger-tent party with a number of easily corporate-compromised representatives in both Congress and Senate. Republicans had an easier time staying unified, although now they do so out of fear of being primaried and voted out by an ever smaller, ever nuttier primary voting base. They'll even buck their corporate interests (tariffs, anyone?).
Pelosi has achieved that unity--with no defectors among the party. That gave Schumer the wherewithal and cover to demand the same of his peers, notwithstanding the Joe Manchin's of this world.