The Florida coast isn't defined by a huge, meandering river. Take a look at some satellite surveys that showcase how the Mississippi River changes over time. We've of course damned up the shorelines upstream where people live in places like New Orleans so there's no inherent seasonal risk of mass flooding, though of course lose the deposited silt and hence further erode the land we've "saved". Further down south toward the mouth, it's marsh land defined by however the river chooses to meander. I'm not sure where exactly SpaceX is planning to setup in LA, but the entire coastline there is chronically very poor, very unpopulated, and not supported to weather flooding of any kind, especially not hurricanes.