Why not just do Medicare For All?
Nobody who relies on Medicare would say that. The people who say it want a fantasy Medicare that doesn't exist.
https://www.medicare.gov/providers-services/original-medicar...
Some of the items and services Medicare doesn’t cover include:
Eye exams (for prescription eyeglasses)
Long-term care
Cosmetic surgery
Massage therapy
Routine physical exams
Hearing aids and exams for fitting them
Most dental care: In most cases, Original Medicare doesn't cover dental services like routine cleanings, filings, tooth extractions, or items like dentures.For example the eye exams for glasses are usually done at the store where you buy the glasses and included in the price, dental might be covered only for children, routine physical exams may not exist as a concept, etc.
Most of the complaints around Medicare come from those who get sold (conned) on takin Medicare “Advantage”, which is a privatized option for Medicare that denies a lot of coverage.
So if the MA rate is less than the provider changes then the insurer is highly incentivized to deny you coverage. While for Medicare you'd have a higher co-pay.
This also leads to scenarios where MA insurers upcode patients so that the treatment is at a higher rate [1]. (ex. Marking patients as recovering drug addicts when prescribing opioids to get both money from both counseling and the opioid treatment).
[1]: https://www.healthcaredive.com/news/unitedhealth-grassley-me...
BTW There can still be a for-profit, premium health insurance market alongside. if you’re rich spend as much as you want on healthcare.
My objection to that is putting too much power over healthcare in the hands of the Federal government ends badly when someone like RFK Jr is in power in the Federal government.
My ideal is closer to the German system, with state-level public options which preserve private insurance.