I'm in favor of the legislation, I'm aware of the overall popularity of it.
Your characterization seems highly unfair to me.
The Ds were not negotiating (fairly clear from the get-go).
Each Senator faces their voters every re-election.
Each might have found at least ONE provision (600+ pages) that wouldn't 'fly' with their constituents.
The legislation is overwhelmingly popular. Surely all senators have large numbers of constituents who are in favor of it.