You noticed!
Yes, I had the same thought after reading about brown cubic rot a couple weeks ago, somewhere on this site.
Thinking about how cubic rot would be useful in a container or irrigated vegetable garden has my mind quite confused though.
I went out and got some and put it in a bowl of water to see how it wicks.
It is very hydrophobic. In this picture the pieces in the front of the bowl have been floating for 2 days. The 2 pieces in the back of the bowl were just put in.
The cubic rot log is on the right, and just a redwood stump is on the left.
Dry redwood seems very similar to brown cubic rot, very hydrophobic and lightweight.
So how is this good for the soil:
* It absorbs water very slowly, so maybe it will release it very slowly. Useful in a drought situation, to keep plants just alive.
* Maybe roots could attach to these cubes and access the air. The cubes would provide better aeration?
However unlike say perlite, when you water the soil, the water won't go through the cube providing an air flush, so the aeration won't be as good.
I'm going to try adding cubic rot to some small container plants and see how the roots attach to it.
It could help make seedlings more transplant shock proof.
Anyway, just thought rambling here.
If anyone has links to good articles on cubic rot, please share them. I've only been able to find ones describing how it is formed, none on why it is so good for the soil.