When you ask yourself why the Democratic Party doesn't in fact do things that you think would be obvious ways to further it's goals and purpose, over and over again, for generations, you might want to start pondering this concept:
Dems have not held power in the US since at least Reagan, Full Stop.
"51" senators (when at least two aren't even democrats and one routinely votes against the party for his literal coal lobbyist cronies) isn't Power.
The one time Democrats held some power for about FIFTY DAYS, we got the ACA. We could have gotten medicare for all but a "Democratic" senator refused. Medicare for all has been on and off the Democrat platform since before RFK got got.
That so many "liberals" and "leftists" insist the democratic party hasn't done anything despite fifty years of being explicitly voted away from the reigns of power is part of the problem.
Go look at the coalition FDR had if you want to know what it takes to push Progressive policy in the US system.
https://en.wikipedia.org/wiki/The_purpose_of_a_system_is_wha...