The reasons aren't always excuses, but if you take on the responsibility for leading things, you have taken on the responsibility for getting things done. There are carrots and sticks, and while no one is all powerful, if Chuck Schumer isn't promising to shit in Joe Manchin's Buick (or offering to move the Pentagon to Wheeling), he isn't doing all he can.
Another problem is we have driven out all the good political corruption and replaced it with the bad kind. Good political corruption is "shower money for infrastructure on my districts and state and I will play ball." Bad political corruption is... I whatever the fuck is going on right now.