Surely "sur ce lit" is acceptable as well. Unless the person in question is literally stitched right into the mattress... in which case I can understand why they sleep poorly.
I have the same question. Why not "sur ce lit?"
you can jump ON the bed, sit ON the bed, lay your dress ON the bed, but you sleep IN the bed, under the covers; just as you do in english.
wondering why "je dors tres pauvrement dans ce lit" not accepted
Why 'poorly'? Someone might feel sick or poorly, but one cannot sleep poorly. I think you meant 'badly'.
We can use 'sleep poorly' in English.
However, one of the word prompts for 'poorly' is 'pauvrement', but wasn't accepted in this example.