As mentioned already, there is hardly any content for a 4K TV. Nobody broadcasts 4K, and there is no 4K cable provider either.
While there are 4K movie theaters, and some productions are really shot and finished in 4K, most are not. And the current model of the most professional and widely used motion picture camera, the Arri Alexa, is not 4K.
Will there be a 4K ALEXA?
[...] Given that 4K digital workflows are still in their infancy, and that for the foreseeable future most productions will finish in 2K or HD, ALEXA is the perfect choice for theatrical features as well as television productions. Furthermore, the ascendance of 3D has resulted in a doubling of image data volumes which further complicates the effective storage, processing and movement of such data. So, for the foreseeable future, ALEXA is ideally suited for 2K or HD workflows in 2D and 3D.