Looks nice. Why they don’t sell PCs with cooling like that? What are the downsides?

Incredibly unwieldy. Real quick estimate of volume puts that at around 1.75kg of copper, so it wouldn’t be possible to mount in a vertical PC case orientation (ie the majority of consumer PC cases) without significant (expensive) modifications to both the mobo socket mount and the case, else its weight would snap the motherboard, or just slowly flex it until traces failed.

It may not even be able to be used vertically like that for very long or it will compress and damage the CPU / socket / mobo. Just as an example, the weight limit of the thermal solution (HSF/water chamber heatsink/etc) for socket LGA 1700 is 950g.

Real quick estimate of volume puts that at around 1.75kg of copper

I assume it’s at least ~5 cm × 5 cm × 15 cm. Given the mass density of copper 8.96 g/cm^3, its mass is at least 3.36 kg.

i find your estimate to be overed

It begins with the question: How wide is the cpu?

Based on that, it’s approximately 3× as tall.

(if you notice the space bar, i think it’s a tiny computer)
I’d say, the copper block is ~3 USB connectors wide
i’d say about 2, @2.4 cm total then…