They didn't have those majorities for a long time. Runoff elections and deaths gave them a two month window or so. They passed Obamacare with that, and had to remove a single payer option to get the last necessary votes.

But also, the Democrat party was a lot less left in those days. There were a lot of Manchin types of conservative Democrats. We've never had the votes for electoral and ballot reform. We needed to build on our majority in 2010 to do it, and we instead we lost the majority entirely.