All the NUCs and other mini PCs I see run mobile processors.
It’s a shame because a simple downdraft air cooler with a 120mm fan can handle a pretty high power load and could definitely fit in a tiny space.
Add a few thunderbolt ports and you could have a capable and upgradeable little pc.
Have you looked at the size of the latest videocards? That’s just the GPU (and secondary components), and it’s bigger than a NUC. The power supply needed to feed a powerful GPU and CPU is larger than a NUC. There’s a lot of empty space inside a modern tower case, but you’re not shrinking high end components down into a NUC. It’s just not feasible.