>I don't understand what medicare for all seeks to accomplish that isn't already available with medicaid.

Medicaid is only available for the extremely poor; Many states have expanded this after the ACA passed, but my understanding is that there's still a pretty good gap between where you qualify for medicaid and where health insurance is affordable in much of the country.

I don't know if you're joking or not but:

Medicaid only help the poorest. You need to be at a certain income to get it. I am a graduate student that is currently on it.

Medicare-for-all helps everybody regardless of income. Everybody is entitle to it regardless if you're poor.

To wit; 400% of the poverty line (spoken as another grad student who was on Medicaid for most of the year)