Floridians love to vote absentee, and a not insignificant fraction of these voters have already cast their ballots for Jeb Bush before the hapless Jeb pulled the plug on his campaign. These are votes that likely would have gone into the Rubio column.
In addition, Floridians love to vote early in-person as well. Sixteen of Florida's 67 counties opened up their polls for business on February 29th, all of the polls opened by March 5th, and over half of the voters in Florida will have already cast their ballots by the March 15 official election day. This means that the avalanche of TV ads and sleazy hit piece mailers that Rubio and his Anti-Trump Super Pac will soon be unleashing will have already missed many of their marks (pun intended).