I’ll answer for me, and 70% of Americans:

1. It was the only plan offered by my employer. Vision and dental insurance are typically optional extras, but medical is mandatory. Some jobs provide a choice between one or two different insurances, or a good/better/best plan. My wife (who is on a different plan than me, because she works elsewhere and neither of our jobs covers family members at a reasonable discount) selected the “better” option because she takes a few prescriptions and it works out to be cheaper long term.
2. N/A (but the answer is the affordable care act)
3. Insurance providers have a website where you can search for “in network doctors” by specialty. When I joined my current network, there were exactly two primary care doctors within 20 minutes of my home. Vision (which is separate insurance, generally) is often much easier to find. Dental (which again is separate insurance, often) is usually even harder to find a provider, in my experience. At my last job I could pay $200/month for insurance accepted by a dentist in my town, or $12/mo for dental insurance where the nearest dentist was over two hours away.
4. I would prefer the entire system was scrapped and replaced with government healthcare at low to no cost, including prescriptions, dental, vision, and mental health.

I’ve been an immigrant for about 25 years now. Not sure if that counts, but I’ve been slacking and haven’t gotten a citizenship yet, so… probably?

I can confirm that I’ve up until now always been on one of the health plans my employer made available to me. It certainly made things easier that I was never out of job, and all of those jobs provided great benefits (typical white collar computer nerd stuff.)

However, I stopped working last year, and my 18 months of COBRA (a continuation of employer-provided coverage after leaving a job, except you pay yourself the premiums your employer was paying (about ~$2000/month for me)) are running out very soon, so I’m discovering the bizarro world that is US healthcare without an employer plan.

I’ve contacted some insurance brokers to help me find a new plan, and each one of them has tried to push weird non-ACA-compliant plans to me under false pretenses (ie. they’ve actively lied to me about what the plans were.)
Sometimes the awful stereotypes about a profession are awful for a reason.

Which leaves me with the ACA marketplace, where every single plan is significantly worse than anything any of my employers ever offered, both in terms of breath of network, prescription coverage, and geographical coverage. I didn’t mention the famously terrible mental health insurance coverage because it was already impossible for me to get in-network care there even with my employer plan.

And then if you figure out which is the least bad plan in the 100+ sad plans offered to you, and you commit the faux-pas of googling them, you’ll get a deluge of screaming victims of those plans wishing they had picked anything else because their experience was a literal nightmare.

So that’s encouraging.

In specific terms, the ACA healthcare.gov site I linked above lets you put a list of doctors and medications to see which plans support them, and the answer for me is “none.” None of the plans available would cover all the medical care me and my wife are getting on an ongoing basis.
So it becomes a matter of picking and choosing what I’m going to pay out of pocket.
For example, right now I pay $0 for various insulin pens, but a great number of those plans won’t cover those, or cover a little bottle of insulin instead you’re expected to use with disposable needles each time you’ll fill yourself and inject yourself with, and hopefully not fuck it up. Out of pocket, with some “discount card” (GoodRX or whatever), a month supply of the pens would add up to roughly $800. So something that was “free” to us (if you ignore the large insurance premiums) is going to feel like quite the luxury instead.

One of the aforementioned lovable insurance brokers suggested that I create a fake company in order to be eligible for reasonable employer-sponsored plans and avoid this nonsense. Sounds great, except for the whole fraud thing and the risk of getting found out and denied at the time when I’d need it the most (which would probably also be when an insurance provider would look the closest to try to find any reasons to deny a large claim.)

And then, there’s the quasi-scam that targets religious (and/or desperate) people, known as “health care sharing ministries.”
They appear to be very affordable plans with great coverage, managed by “faith-based organizations.”
They are not insurance, and ostensibly claim to simply “share the burden” of healthcare across all their members.
Notably, they are not actually obligated to meet any of the (low) bars set by the ACA, or to simply pay any of the insurance claims their members send them, and so sometimes they don’t. Tough break.

At the end of the day, I’m still going to pick an ACA plan and just pay out of pocket whatever isn’t covered. I just have to settle on a plan, which feels like picking from a set of shrunken and half torn blankets the one to use on my bed.

Anyway… what would I change? Nothing obviously. All is for the best in the best of possible worlds.