Generally, it's due to loose articles, and more specifically, phones. Six Flags this year has adopted allowing the use of filming glasses, but nothing else. Some chains, such as United Parks & Resorts, which owns the SeaWorld and Busch Gardens parks, allow filming with camera glasses as well as an action cam strapped to your body with approval from the park. When you go there, you just basically show them your setup, and they'll sign off on a little thing that you can show the ride operators saying you're allowed to film with the action camera. All it takes is one phone coming loose and hitting someone for major repercussions for both the park and the guest who was filming.