Sure it helps to have it in an off-election year. They needed 60% to pass it. The more people that show-up to the polls the greater the hurdle needed to pass it. It only got as close as it did as not as many folks voted as normally do during presidential election years.
Not if it is the supporters who turn out in relatively greater numbers. Recall that the measure was just 2% short of the needed 60%.
Here are the % of voters in FL by age group in 2012 and 2014. Note there's a double whammy at work against the antis => 1. Young voters are likely to make up a greater % in 2016 v 2014. 2. Due to the laws of nature, voters most opposed are being replaced by voters who are strongest in support.
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2012
18-29 16%
30-44 23%
45-64 37%
65 + 24%
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2014
18-29 14%
30-44 19%
45-64 42%
65 + 25%
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http://www.washingtonpost.com/wp-srv/special/politics/2012-exit-polls/table.html (click on the FL icon at top of page)
http://www.nbcnews.com/politics/elections/2014/FL/I1/exitpoll