In general, the problem is that most employees are accustomed to how their employer-based insurance works and want it to keep working exactly that way. Because they know how to navigate that particular set of challenges.
Employers may also customize their insurance and offer benefits that might not be available in a one-size-fits-all government insurance. In particular, some large employers allow their employees a choice of different forms of insurance. For example, my employer in 2005 offered options with
- No premium from me; a health savings account.
- $50 monthly from me; a Health Maintenance Organization.
- $50 monthly from me; a Preferred Provider Organization.
There were other differences as well, the copays were different, the provider (doctors) lists were different, and the deductibles were different. The HMO was more aggressive about insisting on its own doctors than the PPO. Note that I was paying much less than 28% of the premiums. So averages may be hiding individual differences.
There may have also been differences in coverage. Perhaps one plan covered insulin shots better than another did. I wouldn't know, as I'm not diabetic. Which is another problem. We don't know what challenges individuals are having with their health plans. People may have moved around several times until they found jobs with just the right set of coverage for their situations. They may know that getting insulin, methadone, whatever coverage is difficult. But they have it in their current insurance. Any change and they may not.
I think that we can safely set aside the arguments of something like the Cato Institute in considering what the typical American thinks. The Cato Institute does indeed recommend breaking the employer/healthcare relationship. But they don't make any pretense of that being a popular position.
Most Americans who currently have employer-based health insurance are happy with that insurance. As such, they don't want to give it up for some new form of insurance.
One of the great ironies of the healthcare debate is that most people are happy with their personal options. When you hear people worrying about health insurance, it is either a small minority with problems, or a larger group worrying about the problems of the small minority. Of course, part of this is the nature of insurance. Most people pay premiums and get little benefit.
Here is a Politifact analysis of people's satisfaction with their healthcare. While they found that the 95% approval was at the high end, the surveys were consistently finding 80% satisfaction with at least 42% very satisfied. This should put aside the possibility that people were picking employer-based health insurance as the least bad option. Newer polls show a drop in healthcare satisfaction since the passage of the Patient Protection and Affordable Care Act (PPACA; colloquially known as Obamacare).
One might argue that Medicare-for-all could duplicate these options. It could certainly put 72% of the premium (tax) costs on employers. It could allow participants to choose among multiple plans. But of course if it did that, it would lose the purported benefits of Medicare-for-all. In particular, Bernie Sanders is going around telling people that Medicare-for-all will eliminate billing. That of course is an exaggeration. But what it does do is eliminate the question of who should be billed. Unless of course you put that back into it by allowing for different programs that can be billed differently.
The Kamala Harris plan tries to have it both ways. It will still allow private insurance, so it won't get the billing benefits that Sanders promises. But it will bind those plans with new regulations, so it will still cause people happy with their current health insurance to lose their current insurance, just as PPACA/Obamacare did. It has most of the downsides of both the status quo and Sanders' proposed change.