Don't take me as an engineer, i have nothing to do with engineering or physics,i never learned any of these or something related, I'm only thinking with my logic,which can be flawed (and that's wouldn't surprise anyone),but as i see it,the luggage is spread enough to have less pressure, and I'm pretty sure there are some enforcement within the "floor" of it.
As for the ladder,just look at it,the regular home-ladder "shelves" are connected in TWO points,have a special form to less the bending,while the one in the sketch have only ONE connection,which looks like could be rotated with enough force,and if it's not made with a hard material and have some enforcement below it, it's gonna bend down and break after a while.
Woo! no spell check needed!