Because it's speaking about bread in a general sense. Perhaps the bread that you refer to is in the pantry, where no one else would be able to know of it's existence. If you asked, "Do you want THE bread", the people would respond, "What bread", since they do not know that you have bread. Wow that was complicated.
The verb itself does not have a case, but it is a transitive verb and it does require that the object on which it is acting assume the accusative case (in this sentence, khleb is in accusative).
If I get it right, the partitive khleba would mean "some bread" whereas the accusative khleb would mean a specific loaf of bread
This seems like a partitive expression to me. Why don't you use the genitive?
The accusative case is possible, but I would say that the genitive is preferable. Probably the thing is in the topic title.
The fact it is using accusative in lieu of genitive rather supports "Do you want the bread" instead of "Do you want (some) bread".
Or am I missing something here ?
'Some bread' would have to be in the genitive, like the sentence above; "Ты хочешь хлеба?"
Bring the cases so informative, could we omit ты and use "хочешь хлеб?" in an informal context?
Мир, хлеб, землю!