And when they rot away, that carbon is released back into the atmosphere. Hundreds or thousands of years isn’t nearly enough, we need to take it out of the carbon cycle permanently. These particular machines will last maybe a couple of years, and will probably generate hundreds of times more carbon in their construction and maintainence than they’ll sequester, but it’s a necessary first step. It’s not possible to put the carbon back in the ground where it belongs at a viable cost and energy expenditure without building these machines first.