The Dems only had the super majority because they were aligned with Independent senators, so they didn’t actually have a supermajority.
At least one of the Dems was opposed to national healthcare because he was a piece of shit, and they feared getting rid of the filibuster to pass single payer because apparently Dems don’t understand that the GOP is based on obstruction.
Dems need to get rid of the filibuster so they can actually accomplish things when they hold all three branches. Actually doing things would garner them more votes!