This is a repeat of my post on another thread, but it fits to repeat it here...
1.) both candidates were mediocre, so there was little energy for most voters despite the crazy tv ads and phone calls. Most of the Democratic base was simply not interested: teachers, unions, minorities, college students, women...none were really mobilized by this race and Sink didn't mean anything to them. I'm in a union - Sink didn't talk to us. Sink had lots of people walking and calling, but they were going after the suburbs where most folks already were voting for Jolly. There was no "issue" like women's rights or "stand your ground" or ANYTHING that Sink put forward to attack Jolly. All she said was that she would "work with the other side". That's not an issue. Sink is not a good candidate!
2.) The repubs can count on the retired base who have lots of time and vote straight GOP no matter who is running. The Democrats don't vote (as several others have said).
3.) In 2004, I saw a DRE cast a vote for Buchanan when you pushed Castor. We've had reports for a decade of absentee ballots found in the trash, mailed ballots whose signatures were rejected (by GOP volunteers who do the checking; old folks again), and you name it. You get no help here from election supervisors. ID's are "checked" at the polls, and it intimidates some voters. If it's close, the nod goes to the GOP.
4.) The district is gerrymandered. Even when registered, there are a some hurdles getting ballots by mail, voting early etc. Registration is much more difficult under Rick Scott.
5.) Jolly benefitted from a lot of local veterans and military people who came out to protect their health care and retirement. They heard a lot of false reports that Jolly would help them and Sink would do them in...
6.) The senior citizens did not buy into the "Jolly will get rid of SS" message. They already have SS and they know they are safe...they would react if Jolly went after medicare, but all his ads said that the ACA was cutting medicare. We all know it's not true, but I could not convince the retired neighbors on both sides of me.