And they're not just trying to change your mind. They're also working to get the support of the electorate directly.
Now imagine some of those groups had absolutely superb PR. Literally making childhood cancer sufferers healthy again.
Now imagine, like every industry that wants government influence, they hire your friends into highly paid do-nothing jobs, donate generously when you raise money for your charitable foundation, and so on.
Now imagine they're a big employer. And they've got a whole bunch of jobs. Office jobs. Highly paid high-level jobs. Well paid mid-level jobs. Jobs that employ lots of minority groups.
Now imagine that the most efficient outcome would be to shut down all the insurance companies and nationalise all the hospitals, but you don't have the political capital to deliver that, it'd make a lot of people very nervous, and you're not even sure it'd be a moral thing to do anyway. So you'll probably have to settle for a middle ground that keeps a lot of the existing middlemen fat and happy.
Now imagine, even if your reform is a huge success and goes way better than you have any right to expect, people are still going to die in hospitals, and some people are going to say some of them are your fault.
Now imagine turning a blind eye to the problem has been working just fine for the last 20 years. It'd be so easy to just let sleeping dogs lie...
Look at Obamacare. A lot of Democrats will say that this was a genuine attempt to move toward single-payer, a public option, etc. and that they simply had to make compromises to get what they got passed (a change that undoubtedly helps many people but does so with a regressive tax, and certainly doesn’t simplify anything).
they simply had to make compromises to get what they got passed
For much of that Congress, the Democrat caucus had complete control (with filibuster-proof control of the Senate); they didn't have to "compromise" with a single Republican, hence zero Republican votes.