[amyjess]

H.264 may allow 2160p video, but the 4K UHD standard is more than just 2160p. For example, HDR is absolutely critical to 4K, and the only way to do that in H.264 is to use Hi10P which isn't supported by most devices.

In fact, I'd say HDR is more important than 2160p resolution in that I'd rather watch 1080p HDR video than 2160p SDR video.