I think South Florida disproportionately gets a big share of its Spanish-speaking immigrants from the parts of the Spanish-speaking world that play and follow baseball, not just Cuba. I think the issue is more that when people move to Florida from the rest of the United States, they've already got a favorite baseball team and aren't compelled to follow the Marlins.
I'm not aware of the Marlins ever failing to sell out a playoff game in 2003 or 1997. Win and all sorts of people will come. The University of Miami struggled with attendance for quite some time in the last decade, and now that they're undefeated you see an amazing array of folks at their home games. Everyone in Miami suddenly owns a turnover chain replica.
Substitute "DC area" and "Nats" for Florida and Marlins in the bolded sentence above and you've got a double truism.
