Two things, age first. Among Art Deco Historic District properties, the first twentieth-century district the National Register of Historic Places ever recognized, stand roughly 800 structures of historical significance, most raised between 1923 and 1943. That means a whole district built before the modern plumbing code existed, and plenty of it still carries original-era material behind the walls.
Then altitude, or the near-absence of it. Average elevation across the city is about 4.4 feet above sea level, and some pockets of South Beach sit at nearly nothing, so flooding shows up on an ordinary high tide and not only during storms. A line that fails under a slab has no downhill to drain toward, and salt works on everything from every side.
The third factor is process rather than geology. Anything inside the Architectural District gets reviewed by the Historic Preservation Board in addition to the building department, and the entire city falls inside a High Velocity Hurricane Zone, which limits which products can even be installed.