I believe it is a myth that there are legions of hardcore baseball fans in South Florida, or the whole state for that matter. The state produces scores of top-notch players, but that doesn't mean people give a **** about MLB.
Additionally, the demographic of baseball fans skews older. Many had fixed allegiances before 1993. While some migrated to fish fandom, I'm willing to bet that's a small minority. I can't see too many long term Braves, Yankees, Red Sox, Cubs, Dodgers, Cardinals fans just switching like that.
The Marlins had to capture my age group, say 31-37 year olds now (I'll be 35 in December) who didn't have a fixed allegiance yet. They only made the playoffs twice,winning two titles, but then issuing a fire sale.
They fleeced the taxpayer and destroyed the Orange Bowl.
All of this was also occurring as baseball is decidedly less popular among this age demographic.
I grew up in West Palm Beach. Soccer is far more popular than baseball with people my age from South Florida.
I can't even imagine how few Marlins fans there must be among Gen Z. They needed to do everything right just to compete for fan attention.
What you see is the fruit of doing everything wrong.
/rant