Social democratic policies were also just not as popular in 2016 as they are now. In just a few weeks, a full decade will have passed since 2016.
In 2016, people more or less took American democracy for granted. The voters never knew about the danger that Trump's ideology posed to the republic. This was following eight years of Obama, so right-wingers were thought of as fundamentally just people with bad policy ideas and not people intent on destroying democracy.
Only since then have people really started coming around to social democracy, democratic socialism, and other left-wing ideas. Over time, people have begun to realise, Bernie was right.
It really is too bad that Bernie is so old. He deserves a good retirement, but given the current political climate, he's going to keep fighting for the working class until the bitter end.