Except there would be no need to load a TV with that many pixels because it would be viewed from a greater distance. The reason for the high dpi on the likes of the iPad and the iPhone is because they are portable devices that you hold in your hand and look at the screen from a relatively short distance. Increasing the resolution therefore improves the experience at the small distances these devices are used at.
On the other hand, people don't watch their TV closer than a few feet at most (more likely somewhere in the region of 6 feet or more). At that distance, 1080p resolution is really all you need for screens of that size (probably up to about 50"). As screens grow larger (65" and more), then it makes more sense to look at resolutions like 4K or Ultra HD (or 8K) for those screens when sitting at normal living room distances. But these screen sizes are still prohibitively expensive.