By tying insurance to employment (side effect of some economic policy) the option to shop around was removed. When people are already forced to use the insurance provided by employment so that they can afford it, there is no way for some other insurance agency to be competitive. Then it just got worse over the years.
The ACA attempting to make a competitive market was a half assed substitute for just going all in on single payer, but at least people with the jobs that don’t provide insurance have the possibility of affording it now so it is better. Just getting stabbed instead of being shot better.