I think there may be another issue. It is all very well to poll for individual things in isolation, but nobody campaigns on a single sentence policy position in isolation. You have a number of policy positions that get judged together. You have to talk about paying for them. I saw some analysis claiming that was the issue with Labour's disastrous manifesto going into the last election in the UK. Lots of the policies individually polled well, but taken together they were wildly unpopular. In part, the claim was people didn't believe the free lunch they were being offered was plausible.- Sanders' "medicare for all" (i.e. no private insurance) is possibly the least popular alternative. (More Americans support universal coverage with private options, or even the status-quo, than 'BernieCare')
- While some polls show a majority support for "free college", that support is not universal among all demographics, and the older voters (i.e. the more reliable ones) tend to be against it.
The support for the parts of the far left agenda may be individually greater than the support for the whole of it.