If a voter voted for Rubio in 2016, why would that voter not tend to be a Scott voter.
You can’t apply a presidential electorate to a midterm election. Millions of Floridians who voted for Rubio or Murphy won’t bother to vote this year because there’s no President on the ballot. My favorite illustration of how this works is that Scott Brown won no more votes in 2010 winning a senate race than McCain won while losing Massachusetts in a landslide in 2008.
But beside that, there are other reasons. Plenty of people voted for Rubio to be a check on an expected President Clinton. Plenty of others voted for Rubio because they felt the Republican Party was best aligned with the interests of the Cuban American community. In 2018, Trump has given both groups of voters to reconsider their past choices.