These all have broad public support

That is a big assumption.

Many Americans are climate skeptics or “agnostic,” even more are environmentalism agnostic. People who don’t have to personally deal with social security, slow internet, paying for college, weed, unions, personally going through the criminal justice system and such are often not very supportive of those issues. Reproductive and lgbtq rights are extremely partisan and framed entirely differently for different groups.

Most probably know healthcare is screwed up. But even then, many young people have not experienced serious issues (for themselves or others), and many still have a bad image of universal healthcare. And I know small business owners that are rightly concerned about tax increases.

It’s not that these ideas wouldn’t have appeal if conveyed, but the message is just not getting though.