There is a lot of “invisible” work that party orgs do. If you want to see why big names and attention alone don’t work, look at the Green Party. They have name recognition, ballot access and even get a bit of the vote each presidential election. What they’re missing is the “ground game” that gives the presence in nearly every race in every precinct, and the local engagement to actually win an appreciable chunk of elections every year (not just the presidential years).
For whatever reason, when I’m hearing about Dems in the swing state I’m in, I’m hardly ever hearing why you should be excited to vote for the Dem candidate, but instead why the Rep candidate is so awful that you simply must vote Dem to stop them. Like, there was about a week(?) that Harris and Walz seemed to be coming out of the gate going “we’re gonna be so awesome, don’t even worry about the weirdos on the other side”, but then it became “please, it is of Vital Importance you do not vote for Trump, we promise Harris will be better than him”, and I just don’t understand why they changed.