When a student drops a class in Canvas all their user data is removed including assignments they submitted, analytics, etc. If this were a physical course an instructor would still have access to that student's grade thus far in the course. Being able to see a student's attendance and previous work is important for many instructors' records, including my own.
I'm also concerned that all messages to and from the student are also deleted. This kind of correspondence with students who are at-risk of dropping or failing the class is very important to retain and review as needed both for instructors, students, and counselors.
Finally, if a student retakes my class down the line after dropping I would like to have access to their previously submitted assignments so I know they aren't submitting work from their first attempt at the class and plagiarizing themselves. dropped student