Today we are seeing harbors like Marathon in the Florida Keys packed with boats in August and September when they used to be nearly empty. It was inevitable that a big storm would come along and demonstrate why the old wisdom was to stay north until after November. This is the wisdom of the snowbirds.
When I first started heading south from New England in the 1980s this snowbird wisdom was ingrained in the boating public. We all headed to the Chesapeake for the big Annapolis boat shows around Columbus Day, then meandered south down the Chesapeake to Norfolk around Halloween time.
Yes, we did occasionally encounter the late-season hurricane in those years, but we weren't trapped in a place like Marathon with few alternatives but to ride it out and hope for the best. Between Virginia and Florida there are literally thousands of "hurricane holes" up winding creeks, and with modern forecasting and the usual week or so of warning most boaters can move several hundred miles up or down the ICW to get into a better position.
I understand that many boaters in places like Marathon consider it "home," and if you have a job or kids in school it is very hard to leave when a hurricane is headed your way. But, I can't beat around the bush--that is a bad plan for your life on a boat!
Some estimates are that 75% of the boats in Boot Key Harbor in Marathon were either sunk or blown ashore. I'm not sure accurate numbers will ever come out, but the general scale of the problem was dramatically illustrated during Irma. Marathon is not a good place to spend Hurricane Season!