Thickness is something, length is another thing...
Cannot replace one with another and cannot compare them. You can't chop or baton or cut through wood or anything else which is more than double in thickness than your knife edge length, regardless how thick your knife is. An axe can do that because it has different geometry, but a knife can't.

PS: I edited my previous post, adding an advantage for thickness that I had previously forgotten: thicker means better in wood splitting.