So to my larger point is that Sanders is largely either the only or one of the few candidates pushing for a whole long list of things that everyone in this forum and a majority of Americans would shake their heads and go "yeah that's obviously the right thing to do." But despite their popularity, they have not been adopted by democrats at large.
Could you give some examples of which policies you see falling into this category (most people agree they should be done, Sanders is the only democratic candidate advocating for them)?
You're right we should delineate what is Sander's proposal and what is not. (I'm only going to consider the top 6-7 candidates)
Next to each one I'll see if I can find a percent approve/disapprove/NA poll number
$15 minimum wage. - Actually found that all candidates signed onto this.
Pretty much all agree the defense budget needs to be cut
Unique to Sanders (and maybe Warren):
Economic:
Federal Jobs Guarantee - 78/11/11 (2019) Harris - 52/29 (2018) Civis
Break up big Tech - 60% GOP, 63% Dem., 66% Ind. - 2019
National Rent Control - No polls I could find, but I would assume this one unpopular
Against TPP - 56%/27% (2017)
Foreign:
Open to reopening relations with Syria - Difficult to find but for polls around Syria, it looks like they poll close to 50/50
Would meet with North Korea without preconditions - 41/36/24 (2018 - about Trump's meeting)
Education:
Cancel all student debt (found one that polled debt cancellation for up to 50k polls at 57%)
Free college - 72% (2019)
Ban Public Charter Schools - 39/48 (though 50/50 among dems.)
Climate Change:
Phase out nuclear - 49/49 (2019)
Ban Fracking - 46/33/21 (2019)
Ban Fossil Fuel exports - (hard to find, but Green New Deal polls are very positive usually around 50/33/15
Healthcare:
eliminate private insurance - 41% (most want M4A with private still available)
gov. should produce and sell generic drugs to lower price - no polling I could find, but most any proposal to lower drug costs typically scores around 80/20
I'll be honest, there were a number of policies that I thought would be unique to Sanders, but found that there is a mix. Though I do feel that there is a difference in how much a candidate pushes certain policies, though that is a bit harder to quantify. However, Bernie still holds a number of proposals that are uniquely popular even among GOP voters. This is what I believe helps create his unique draw in the midwest states.
What I find strange with the medicare debate is that if the government has a M4A that was cheaper and accomplished all the same things as other insurance, hardly anyone would use private insurance, but everyone wants the company to be there. We would eventually question it like "why do we still have pennies?" Anyways side tangent.