Why? Most protesters are local to their communities. And if you live in Florida, you get used to the heat. You don't have to like it, but you're used to it.
I understand it's easy to believe the story that protesters are being bussed in. But they're not. At least not from far away. They don't have the money to bus people in. At most you'll get caravans of 3-4 cars from other parts of the state, but the vast majority of the people are from the county the protest is happening in, plus surrounding counties.