If you polled everyone, you would also find that they want lower taxes at the same time they want more services, better schools, etc.
A huge number of people also didn't support the ACA, until they were educated on what was actually in it.
What the public supports in a poll is not always possible in terms of actual policy. I don't think that the poll included being willing to pay higher taxes, the closing of many rural hospitals, and rolling out something even larger than the state exchange websites that will impact your ability to access your health care.
Here is the poll you are referring to broken down - there are those that strongly oppose it as well as some that "somewhat favor" "medicare for all"
Another Kaiser poll also found this: Looking specifically at Democrats, just 5 percent say they favor Medicare-for-all and that a candidates support for it will be the single most important factor in their vote.
GOP candidates would take that as reason to oppose it strongly. And we see how they have chipped away at the ACA over the years. Do you really think that there is going to be support for Medicare for All, once people understand the consequences on the health care system?
There are countries in Europe that achieve universal health care coverage without single payer.