I think this is really the core of it.

I remember that it took months of discussions, compromises and buttering up specific opposition members to get it passed, and that it was a trimmed-down version of the original Medicare plans.

I wish I could remember where, but when answering a question very similar to the OP’s - perhaps in an interview? - Obama explained that he would have very much liked to tackle two big things: health care and climate, but that his party’s resources were stretched too thin to do both at the same time and that he knew they would loose control of the house in the midtems (2011), so he picked one thing.

Table listing who held the house and the senate during the Obama presidency from 2009 to 2017