Rather than asking, “Why didn’t you put your work away?” the adult should state the objective facts with a polite reminder as to the proper action: "Your work is not complete, the materials are still out. Finish your work before starting something new."
Only as needed would this need to be extended into explaining (or not!) a consequence. “I see your work was not put away,” usually suffices to elicit either a verbal or physical response from the child, in the form of an explanation why the work is still out or the child going to put it away.
If needed a reminder might be about the next person who would like to work with that material or in that place; the intrinsic value in completing the work cycle (this is how the environment functions); the natural and logical consequences of leaving out a particular piece of material, which may also include that the child cannot work with anything else until this original work is put away; other responses.
Provide these as needed. More often than not, provide them in a grace and courtesy lesson.
This is in direct opposition to most non-Montessori child development programs being promoted throughout the