14 voted present, all Democrats. My guess is not for the reason you suggested but because of fear of consequence.
Another way to handle this in my opinion, would be for every Democrat to have voted no and to have made it clear the reasons were that the bill was put to a vote by Republicans as a means to end provide any kind of social security.
This may be just me, but I object to the entire exercise of putting ideological labels on everything. I support a set of policies, not an ideology. And I support the policies I support because they fix problems and make people's lives better, not because they're ideologically correct.
It's also the case that governments vary by degrees to which they involve themselves in their nation's economies. On one extreme is total government ownership of the means of production, a centrally planned economy, and no private businesses. On the other is the kind of laissez-faire capitalism of the 1880's that modern libertarians pine for. Where government does nothing at all except enforce criminal codes and provide for defense of borders.
The truth is, the US and every other developed country is somewhere in between those extremes, and we're actually nowhere near either extreme. Socialism isn't a static concept of you have it or you don't. We're less
socialist than Europe and Canada but more
socialist than conservatives want us to be. That socialism v. capitalism is a spectrum is absolutely correct: it aligns with objective reality.
But conservatives have never been much about objective reality. If they were, they'd attack the policies on reasonable grounds and avoid the labels. This crap is just a political game where they slap a categorical label on a bunch of policies or just policy ideas because they know the label has a negative connotation for conservatives and some swing voters.
I wouldn't play that game with them at all. It's smart not to. Sanders should never have self-identified as socialist. All he had to do was state what policies he supports and why. It's just as honest, less confusing, and way smarter.