I think your timeline is off. Miami experienced their dominance in the 80s while Florida was pretty much irrelevant. Florida didn't start becoming a top tier program until the early 90s while Miami went on a downward spiral they didn't dig out of for much of the 90s. I can't say I remember any sustained period of time that all 3 of the main Florida schools were dominate simultaneously. Now with Taggert at South Florida and Central Florida on the rise, it make it even more difficult for any of the Florida schools to be the dominate programs they once were.
I see what you're saying...but Miami had some really good teams in the 90's and the early 2000's when all 3 programs were strong. As evidence:
1990-91- All 3 schools lost 2 games
91-92- Miami went undefeated, UF/FSU lost 2 games
92-93- Miami lost 1 game, FSU 1 game, UF 4 games
93-94- Miami lost 3 games, FSU 1 game, UF 2 games
94-95- Miami lost 2 games, FSU 1 game, UF 2 games
95-96- Miami lost 3 games, FSU 2 games, UF 1 game
96-97- Miami lost 2 games, FSU 1 game, UF 1 game
97-98- Miami sucked, FSU 1 game, UF 2 games
98-99- all 3 schools lost 2 games
99-00- Miami/UF lost 4, FSU undefeated
00-01- Miami lost 1, FSU 2, UF 3
01-02- Miami undefeated, FSU 4, UF 2
Pretty solid stretch where the schools were in good form for the most part.