> Why do candidates need to "spread the message" and "go on tour" and "win people over" when we as citizens are supposed to, at the root, be voting on what policies they believe in (which seems concrete + fact, instead of something like leaving a wooing/lasting impression with a speech/appearance)

That assumes that citizens are supposed to be voting on policies. In our representative democracy, we vote on the people we want, not policies. The specific policies will be unrecognizable after they get through the process of political compromise. What people are really voting for is the person whose hand they want on the wheel.