Visibility via advertising puts the candidate's name in people's minds. That way when people go to vote, assuming they're not the typical mindless drone that just goes down the ballot and checks all the democrat/republican boxes, they vote for names that sound familiar. Because they're more likely to pick a name they've heard of than one they haven't. That's how you buy votes.
Indeed.
Most people don't have the time or don't care enough to go look at all the options they have. As such, they stick to those they've heard about, and chose their favorite according to the information that was fed to them. This is in addition to the "not wanting to waste their vote on a candidate that doesn't have a chance to win" mechanics I spoke of earlier.
