1) national health care plan
First, it's not surprising that people want "some kind of health care". The system is a mess and gobbles up tons of money, including government spending.
Taking the OP's cited poll:
A majority of Americans agree with many of the Democratic presidential candidates in favoring some type of national health insurance plan, though most Americans still like the health insurance they currently have and do not want private insurance to be replaced by a public option.
Meanwhile, more Americans today approve than disapprove of the 2010 Affordable Care Act, though many — including most Democrats — now think the law didn't go far enough.
As a Canadian, I agree, Obamacare did not go far enough. But if you read the poll, "most Democrats" does not equal "most Americans". And 48-49% of American voters, in 2012, voted for a platform specifically wanting to repeal Obamacare.
Second, there were significant forces against going much further, including on the Democrat side of things. Workers that are unionized, civil servants or work for big companies often have pretty good health plans already. It was not appealing to them to ditch their plans for a nationwide system.
On the Republican side, many label any single-payer plans as Socialism, by which they really mean Communism. Never mind that US government spending is on par with other countries running a real national plan. So it really does get a lot of grass roots pushback, including from people who would benefit. Substance? No. Image. Yes.
In psychology, it is common to privilege aversion to loss over hope of gain. The US system is so messed up but also so impactful to individuals and so costly that many people will resist change in case it makes things worse.
Finally, the OP has a lot more ambition for their health care plan than the poll they cite: Biden does not have a national public health care plan. Neither did Obama. Bernie Sanders did, but he is not a democrat. – Beginner Biker.
(2) increased taxes, not fewer taxes, on the wealthy;
A new poll is finding broad support for an annual wealth tax on people with assets of at least $50 million, underlining support for taxing the rich.
That's pretty much what one would call both a softball and two wolves and a sheep voting for dinner.
Is this typically the kind of tax increase that usually gets proposed? No. One Obama tax increase proposal started dinging up people from $250K on up. Not $50M. There the resistance towards tax increases becomes much more pronounced.
This particular poll might pass. Would it solve budgetary problems? Well, likely wouldn't hurt (but keep in mind France's impot sur les grandes fortunes / special-rich-tax never made much money).
Ideally, a broader tax increase would be sought, not just on the very, very wealth, but on the reasonably wealthy. And maybe tax capital gains more aggressively while you are at it.
That's the kind of tax plan that gets pushed backed, not rose-colored ones like this poll.
(3) and more, not less, environmental regulation, particularly on climate change.
WASHINGTON, D.C. -- The majority of Americans say protection of the environment should be a priority, even at the risk of curbing economic growth, and believe the U.S. government is not doing enough to protect the environment. About three-quarters support spending more government money on solar and wind power, and support higher emissions and pollution standards for industry.
Over Six in 10 Say Government Doing Too Little on the Environment
Sixty-two percent of Americans currently say the government is doing too little to protect the environment, the highest in 12 years and well above the low point of 46% measured in 2010. The only time when the "too little" percentage was higher than 62% came in 1992, when Gallup first asked the question.
This is, again, a rather softball poll. "We ought to do something" seems to be the idea.
I am going to counter with Washington state's rejection of a carbon tax. This is a largely Democratic state, with little fossil fuel interest.
When push came to shove and it came time to vote, people voted against a $15/CO2 ton.
We are hitting the limits of this kind of poll here. While people may want to "protect the environment" in the abstract, they most certainly also have an aversion to paying for it. Or to modify their consumption habits.
This is not a particularly novel problem
Any democracy can have a majority of people who feel "somewhat for" issue X. This will show up in polls.
However, if a minority of people feel "strongly against" issue X, they can influence the vote by lobbying, funding. And they are more likely to treat this vote as single-issue and vote for whoever is against it.
Even in the corporate world that holds true. A number of corporations have indicated they'd prefer better, predictable, climate change regulations. But the ones really at risk, like the coal mining companies, will fight it much more than the somewhat-support camp.
In the US, there is no better example of this strong aversion vs moderate support imbalance than gun control. Any concrete proposal to limit guns is going to be fought tooth and nail by the pro-gun supporters but will only be one of many policies guncontrol-supporters will evaluate while casting their votes.
It would be ridiculous to argue that it's only corporate gun interest that are keeping the US gun laws as they are.
A small-ish minority of very committed voters beats a diffuse majority of "we ought to do somethings", especially when they can can exploit US ideological fault lines to do so.
And a politician ignoring this would not get elected.
Last, governing by polls - the gist of the question - is not a particularly great recipe for good government.
In fact, I would myself be for all 3, but I don't confuse my preferences with the capacity of a government to get elected and effect policy on such a platform, not without considerable negotiation and finesse.