The question isn’t why we ended up with a worse bill than we should have. The answer to that is clear: we only have 50 seats in the Senate, so we’re stuck with pleasing the most conservative Democrats.
The question is: how do we get a majority in the Senate that keeps us from being beholden to the most conservative Democrats.
Sadly, progressives don’t win swing districts. Progressives win safe districts, and replacing somewhat progressive senators with very progressive senators isn’t going to change the fact that any bill Joe Manchin doesn’t approve of won’t pass the senate.
What might change the equation is DC and PR statehood. But for that we have to get rid of the filibuster and guess who opposes that? Joe Manchin.