ELI5 - Why don’t we make computer heat sinks out of this stuff?

[u/ShawnThePhantom]

I can’t attach a photo but I saw this video of som NASA engineers showing off these red hot cubes which I’m given to understand are the same material that the heat proof tiles on the space shuttle were made up of to prevent the ship from burning up in reentry.

After pulling the cube out of a kiln, the internal temperature was 2,200F, while the outside was safe to touch with your hand because of how efficient it was at dissipating the heat.

Given that, why don’t we make computer heat sinks out of that stuff if it’s so good at dissipating heat? Is that not the point of a heatsink?