A big part of it was the overall national picture. Florida is often around R+3, and since Bush won the popular vote by around 2 points, you'd expect Florida to end up this way.
This was of course different from 2000, though, where it was the tipping point state, so I'm sure it was shocking at the time (I was only an 8th grader so I don't remember, even though this was the beginning of my political nerdiness).
Yeah, it's understated that 2004 was the first and last time after 1988 the GOP won the popular vote. For perspective, in 1988, FL went red by north of 20 points. In 2008, 2012 and 2016 FL voted about the same to the right of the country as it did in 2004, only the Democrats won the popular vote by at least 2 points in each election, keeping the state very competitive.
