Schools and universities often needs documentation for exams and assignments. If teacher uses annotations in assingnment, these annotations have to be documented also.
The download option in assignments covers only the submitted documents. There is no process to download all annotated submissionsin one step by a teacher. In large classes there are often 25 or much more submissions in each assignments.
It should be possible to download all annotated PDFs in a one step process like students sumbimssions.