The reality is the democrats can't reform the supreme court, because they don't control the House of Representatives, and barely control the Senate.
To enact reform of that type they would need solid majorities in both chambers and control of the presidency. That remains very unlikely. Even simple ideas like expanding the court rather than meaningful reform is impossible as no nominees would get through congress.
It makes sense the democrats make their campaign focused on Donald Trump. And as bad as the supreme court is at the moment, the democrats have bigger issues to deal with - a lacklustre campaign with a poor candidate. It'll be hard enough trying to convince people Biden is a good choice as a candidate, let alone move into complex areas like judicial reform.