People had the same argument about 4K from 2K and the same argument about frame rates higher than 60fps. But, the bigger counter to that argument is that even if that were true, additional features take up additional bandwidth and the true power of these new connector standards is in the additional bandwidth. Things like 4K HDR at very high refresh rates and additional features like 3D and VRR can have signal room on the same cable enabling the creation of displays that can do more at once than they could before. Also there are high pixel density displays and projectors that can make use of 8K and 16K footage. It's niche for now but the technology advancing is not a bad thing.

One use is VR, where the field of view is huge. The industry size and distance recommendations have a TV take up about 30° of your field of view, which works out to 128 pixels per degree for a 4k screen. For a headset with a 100° field of view (most are a little higher than this at this point, or at least claim to be, but it's a good baseline) you'd be looking at a 12k resolution to get the same level of clarity. But, of course, you'd need to run it at a very high framerate to avoid simulator sickness, whereas 4k often gets away with just 30 fps. Delivering power over the same cable also means just one cable.

Currently there are no GPUs to drive that high a resolution and framerate. But the cable was one limiting factor there, made especially frustrating by nVidia sticking to displayport 1.4 for so long.

High refresh rates and VR are 2 uses I can think of.