The historical reason for why it's tied to specific jobs is because salaries couldn't raise for a period of time in US history and so jobs started offering other perks, like paying for all or most of your health insurance.
Now, companies get group discounts and still (often) pay meaningful percentages of many employees healthcare, and so getting private insurance is a nonstarter.
It was less concentrated industry before the ACA.
the fundamental reason is as usual: too much government regulation that was erected with good intentions, but ended up becoming a competitive Moat that reduced the competition and entrenched big players. With that amount of regulation healthcare should be universal like in Canada or UK.
To maintain private healthcare sector, there should be less government
While I agree with this, that regulations are often championed and even written by entrenched companies to increase the barrier to entry, the government can sue to block any merger they deem a harm to competition. Unfortunately they choose not to.
AI is a good example of this. If the government regulated AI, the only companies who will control and profit from AI are the ones who already have it.
To be fair, ACA passed, and here we are. Healthcare companies are making more than they ever did. Have you considered that powerful propaganda machine works both ways?
https://www.axios.com/2024/08/08/insurer-profits-health-care...