Because that's the way state sales tax works in the US. You don't have to pay sales tax on products that are shipped to you from another state unless the business also has a presence in the state where you live. Disney's Fine Art Photography has no offices outside the state of Florida.
If they delivered the products to you while you were still in Florida, you would have to pay tax. But it takes them 6 or more weeks to prepare the photos from a Magic Kingdom Bridal Portrait Session.