Because the whole concept of the video is so complex that it's not very easy to understand it. For most people, it's just Katy in some weird alien outfits lip syncing to her song.
But the video illustrates the journey of an extraterrestrial creature to Earth, who wants to find her lover, the only survivor of the Apocalypse, which is held captive on Earth.
While falling to Earth she looks for images and information about what life used to be on Earth before so she could understand her lover better and get closer to him.
She finds him, her love sets him free and they walk into infinity.
Its cinematografy is amazing, the editing and special efects are breath-taking. It is a masterpiece.
In my opinion, it's the best music video of the last 10 years.
