Helmets in Florida are optional for adults over 21 years of age and in Key West most people take advantage of the law. I don't think its unreasonable in light of the fact that we have no tax payer funded single payer system so breaking your head may very well break your bank, not mine.
This easy going attitude to riding drives people from elsewhere crazy sometimes. I think there can be a little too much stress on the notion that passive safety is more important than active safety.
Which is not to say these flip flopped riders don't sometimes ride drunk, or get into wrecks and from time to time break their heads.
Key West makes for a lovely back drop for vacation pictures and the heat even in winter can overwhelm people not used to it. What seems like a fresh humidity-free winter afternoon to me seems cloyingly hot to someone who was in a snowdrift 2 hours earlier.
I like how bicycles and scooters are daily transportation in Key West used to get dogs to the park, groceries home from the shops. I see renters enjoying scooters on their visits, and riding bicycles too but these pleasures they don't take home with them and start a new way of traveling at home.