I can see where you would come at this as that type of issue. And it is the administrative side of course management, but in many institutions that is part of the teacher's job as well (k12 comes to mind where the student isn't as technically savy as the teacher). And they don't have the same separation that Moodle imposes in assignment. Teachers are allowed to touch grades, feedback and submissions. Again it isn't really different than quiz's use case to remove attempts and Moodle allows that.
The key does come in storage management, which is a big issue for most clients. Photography and video courses can have submission sizes in the 50 MB to 1gig range with current 1080p and 15-20 mega pixel cameras. My cell phone can make a 300 mb compressed file in roughly 5 minutes. Multiplied b 30 student's in a course and you are in the 15-30 gig range of storage. Multiply that by 3 or 4 file submissions and you are in the 45 gig to 120 gig range of storage for one course. That becomes a very costly proposition.
There needs to be some way for a user with a permission to remove submissions without requiring the student to get involved, because a student won't care about the storage requirement unless it costs them money.