President Clinton, Obama and Trump have all promised single payer health insurance. Why do politicians fight this from happening?

Well, I for one do not want a state-run healthcare system. I'd much rather have private health care under a market system.

Lots of money fighting them from the health insurance and pharmaceutical industries.

And Trump never once promised a single payer system.

Two reasons mainly

or more to the point

Single Payer has a bad effect on two basic parts of US healthcare:

Healthcare Insurers who will pretty much be eliminated, or if they would exist, would work as government contractors.

Healthcare providers (Doctors, hospitals, drug companies etc) who would lose tremendous power and money under a single payer system.

Follow the money behind the lobbyists against it, and you will have your answer. Spoiler alert. It's the insurance industry and big pharma.

No, we pay too much taxes already. I don't want to pay more so illegal aliens and lazy liberals can get healthcare they feel that they're entitled too.

because it does not work.

Bernie is at it again -- touting "Medicare for All" ("M4A" below) without any mention of the costs or where the money might come from. That only lets the Republicans shoot it down again. So, where can the money come from?

Details:

"M4A" would have to buy out the existing health insurance operations. Estimated one time cost ~$800 billion.

"M4A" would increase the government's annual costs under existing rules by about $800 billion per year.

"M4A" would also require increasing Medicaid payments by some 20% so that patients are on any equal footing -- estimated annual cost $100 billion.

And, "M4A" would need to increase all Medicare payment schedules by an estimated 25 percent so that our hospitals and physicians do not go bankrupt. Estimated annual cost [after expanding the program] ~$650 billion

Total annual revenue goal is then $1.55 trillion plus debt service on the $800 billion (let's call this $50 billion, ok?) for a grand total net revenue need of $1.6 trillion per year.

ok -- Where can America raise taxes by a total of $1.6 trillion per year -- and actually collect that sum?