They were trying to get Republican votes so that the law would be bipartisan. In the end it passed on a party line vote, so maybe the compromises were a mistake...
The parties weren't yet ideologically sorted. The Democratic majority included dozens of members of the Blue Dog coalition, a conservative group who (among other things) didn't support healthcare reform.
Also the us Congress is blocked by the senate needing 60 votes/supporters to reach cloture on every single bill, except the once per year thing that got the bbb passed. So it's very easy to block the other side. https://en.wikipedia.org/wiki/Reconciliation_(United_States_...
All the Democrats bought by the private health insurance companies I assume.
Democrat senators Lieberman and Baucus mainly torpedoed it. And Pelosi refused to get republicans on board.