Diatomaceous earth is a powder product that is like small rocks. These small rocks are sediment of fossilised algae.
Diatomaceous earth kills bed bugs by eroding away at the waxy layer of their outer shell. Bed bugs will need to crawl through enough of the earth to erode away enough of there shell to kill them.
To use diatomaceous earth effectively the earth would need to be used on all paths bed bugs are taking to get to us. Due to to how the earth works, bed bugs may need to crawl through the earth multiple times for the earth to be enough to kill them.
Bed bugs feed every 7-10 days and this would be the main reason they would crawl through the earth, in search of us, their food source.
Bed bugs are also lazy and will try to hide as close to us between feeds. This creates a shorter distance for the bed bugs to crawl through the earth meaning they will crawl through less diatomaceous earth causing less damage to their outer shells.