Once again.
There are primary interests each faction has. Its most important desires. And then there are a thousand smaller ones that would be nice to have.
The way it works, basically, is that it's pay to play. That's the entrance fee. Donate to parties, PACs, candidates, hire a party's former members and staff as lobbyists, and so on.
Once you have done that, you get to be heard about what you want. But those wants don't include, 'oh and destroy that other donor to save me a few bucks'.
As I explained, the interest in companies not paying healthcare is far, far less than the healthcare insurance industry's entire existence being based on not adopting single-payer.
So you want to say, 'a bunch of companies who benefit from single-payer are less powerful than one industry, healthcare'. But they aren't all pushing for that as their main desire. If they were, the many donors WOULD get their way. It's a minor, 'nice to have' for all of them, and the top priority for insurance. And that means, they get the other thing they want as top priorities, and insurance gets its top priorities.
They all come at the expense, pretty much, of the American people, whether in terms of money, or rights, or protections, or public resources like the environment. Subsidies, blocking regulation, destroying the environment are all things the donors can get at the expense of the American people.
Think of an analogy. Each branch of the armed forces gets spending on things it wants that are arguably excessive. Now Army could say, 'use our influence to cut waste on Navy spending, instead of getting us a bigger budget'. But Army doesn't care about Navy waste as much as it cares about its budget. So it fights for things for itself, and doesn't mess with Navy. Companies fight for their desires, not a more minor priority like single-payer.