Their source tells them that apparently Apple still feels that 4K is still in its infancy which we suppose makes sense. There isn’t a lot of content available in 4K at the moment, and adoption of 4K displays/TVs isn’t that widespread yet. However some have expected that Apple might have been interested in future-proofing the Apple TV by enabling 4K video support.
After all it was discovered that the A8 chipset in the iPhone 6 and 6 Plus are capable of 4K video playback, so why wouldn’t the Apple TV, right? That being said, they have also pointed out that streaming 4K content from content providers is also expensive due to the amount of bandwidth consumed, not to mention not everyone will have the connection needed to stream such content smoothly.
This doesn’t really come as a complete surprise as Apple has been known to be slow when it comes to adopt existing technology especially if they think it’s not “ready” yet, like how long it took before iPhones had front-facing cameras and it was only in the iPhone 5 that Apple finally enabled LTE connectivity.