Because it's a far right party. Trump happens to be more far right, but that doesn't change that fact. I'm not voting for far right, neoliberal, genocidal freaks.
At how many genocides do you draw the line? If the democrats committed a second one along with the Palestinian genocide they are committing right now? You'd again say trump would be worse, vote for Harris. If they committed three? Four? No matter what they do, Trump would do worse, so again you'd tell us to vote for Harris.
I draw the line at a genocide and at everything this neoliberal party stands for. I am not giving that party my approval because it is going in the exact opposite direction of what I stand for. At some point, the lesser evil is too evil.