There's absolutely loads of footage of 9/11 that exists but has never been shown to the public. New videos are being released all the time as the people who own them choose to upload them to the internet. For various reasons, both private and otherwise, some of those people have waited more than 20 years and all they shot was camcorder stuff. So, with that in mind, why on earth would the security team working at the very symbol of the US' entire military complex release sensitive CCTV camera footage of their own site to literally the entire world? How much information that would reveal to the wrong forces doesn't even bear thinking about.