A few things....
All things being equal, Disney had two options. (They might not have had any as this is an off the shelf system) Galvanized or some form of paint.
Paint would look better to start, but there would be a near-endless cycle of repainting to not only keep the appearance up but to keep the supports from corroding. Given that parts of these towers are mechanical systems that you most like don't want to indiscriminately hit with a paint sprayer and that a number of them are located in less than ideal locations for regular access, regularly painting them would be a daunting task.
There is also the issue of when you paint. Painting outside at night in Florida when dew is settling on ever surface the moment the temperature begins to drop is doable, but not exactly ideal. That potentially forces you to paint during the day which means downtime for a system that needs to be up and running 365 days a year.
Being galvanized is largely a one and done deal where you only really have to repair physical damage to the coating.
Given those two options, I would lean towards galvanization as the better one.