Why don’t the democrats support ranked-choice voting, then?
Because they get elected by the current system.
What has Biden done to curtail the genocide of Palestinians?
Helped negotiate a ceasefire that Hamas broke, and has spoken publicly about Israel not doing enough to avoid civilian casualties. Not much I admit, and far from enough, but not nothing.
There is no lesser genocide
The US could send more money and weapons to Israel and publicly support the killing of civilians. So yes, there is a lesser genocide.
People abstaining or not voting democrat in 2016 because they were mad Sanders didn't get the nomination led to a Trump presidency. It didn't help make the Dems move more to the left, it didn't help people get more social services. It just led to a vastly more right wing era that was hostile to minorities, removed many LGBTQ+ protections, ended abortion protections, and enshrined a corrupt supreme court for the next few decades.
But I'm sure you're so happy to return to such a government to stick it to Joe Biden.