The problem is not only the lack of available content, but also the fact that people do not see the difference between high-quality 4K and 8K. This is a natural phenomenon, because according to surveys, a picture size of about 80 inches is needed to see more detail above 4K from a normal viewing distance. Seriously, when will the 80 inch + TV size become mainstream?! This is still years away, and traditional fixed-screen solutions may not even be up to the task due to the complexity of the TV size.
Not to mention that this is not the direction of the game industry either. See, most PC gamers still only play on 1440p monitors, that's the trend.