The reality that Bernie is getting maybe 30% of the vote currently in a Dem primary suggests that either the votes are extremely rigged or that the groundswell of support for social democracy just isn't there. Even if you were to factor all of the ways American democracy isn't really democratic, you could put together an overall poll of the whole population for a whole set of social democratic platforms and run a survey. Individually you can tell people "Medicare for all!" and it polls high (and this is only because the alternative we have now already costs Americans a huge chunk of their income and they're basically obligated to enter the insurance market). But if you put M4A in any sort of coherent framework that you can call social-democratic, which is what Bernie is going for, then you start to see support flagging. There is no magic mix-and-match that gets you everything you want while being aesthetically pleasing - if you want social democracy it implies humanity towards immigrants and a softer hand from law enforcement, and both of those positions are not terribly popular with Americans or really any Euro country.
Medicare and Social Security, the two biggest budget items in the federal budget, are funded by payroll taxes primarily. You couldn't operate those programs without the payroll tax, because it brings in a ridiculous sum of money. The whole point of how those programs were structured was to limit the burden on the rich; and even if you had some pretty confiscatory tax rates on the upper-middle and upper classes, you would still need a payroll tax bump to fund Bernie's program. Bernie himself acknowledges this in his own platform.
Again, you're seeing the results. Bernie at 30%. If you look at politics are arbitrary feels, you create an echo chamber where the whole country agrees with you or they're dumb/evil/etc. But the reality is, much of the country doesn't want social democracy as a whole system. If you did, and there was a huge crossover with conservative voters for this, the result of the primary would be a forgone conclusion beyond any ability to rig. You can't chalk it all up to brainwashing and fluoride. The class that pushes for social democracy just isn't there, for the reasons I described; the middle, educated class don't feel they need it any more and see the lower class mob as an enemy that threatens the status they won in the old system, and the upper class no longer needs to raise a middle class of educated people beyond what currently exists.