It's turnout, turnout, turnout. In close races where get out the vote operations contacting every possible voter, there is no way that likely voter polls can pick up on last minute voters or even have contact information.
Most rational people hate getting incessant calls from political candidates begging them to vote, and just wish the calls would go away. And they hide from strangers knocking on their doors.
I've actually volunteered for a campaign and get out the vote does work, there are plenty of voters who do respond to calls or visits, and get out to vote at the last minute.
