1/3 of people don't vote. They are disenfranchised or politically apathetic. 2/3 of people are propagandized or coerced into voting for parties that don't serve anything besides capital, greed, and their own lust for power.
We need a new system. The concept of "political parties" is harmful to human progress. We don't need people on imaginary teams playing tug of war with each other while the world burns.
What we do need is strong and principled leadership, that is not poisoned by capital or team politics, that is motivated towards improving the planet and actually working to solving critical issues instead of worrying incessantly about "cost" at every single step.
There's no need to play the blame game, but if we want a future that is not undesirable, it necessitates positive action and a willingness to identify what is blocking or stagnating us as a species.
What major figure in Democratic party has seriously fought for this?
No Democrat is seriously looking into real electoral reform that doesn't benefit their party. First-past-the-post will never be changed under their leadership. This voting system allows them to shift blame to voters to the left of them (that they alienate) for voting Green/et. al. They engage in more voter suppression activities than they spend time arguing for serious electoral reform.
https://www.carolinajournal.com/nc-democrats-forced-to-pay-green-party-for-frivolous-intervention
https://apnews.com/article/wisconsin-jill-stein-harris-trump-lawsuit-405e8bae8ff9becfa81a1360708d59a0
https://arizonaglobe.com/legal/democrats-sue-to-block-green-candidate/
https://thenevadaindependent.com/article/nevada-democrats-sue-to-block-green-party-from-2024-ballot
https://dailyinterlake.com/news/2024/aug/27/montana-dems-sue-to-keep-green-party-off-november-ballot/
It goes on and on and on and on if you look at lawsuits and complaints against other parties or look further into the past.
If Democrats had even 1% of the fight that they have against third parties and put that towards positive change and actual solutions, they would've been able to accomplish some of the things you listed.