This doesn't make a lot of sense to me. Yes, having records of what was submitted for multiple test or legitimate re-attempts does make sense. However, there should be some way to remove a submission in the case of a mistake. For example,
Suppose a student uploads, by accident, the incorrect file that includes personal information unrelated to school. As soon as the file uploads and Canvas renders the preview, the student realizes their mistake. I do not see why they should be prevented from removing this file within a few minutes of submission. This seems like an oversight that other learning platforms have dealt with.
There's no reason that a teacher needs a record of their mistake nor access to that file. Depending what the student has accidently uploaded, it may also put the school or Canvas at risk of liability since they need to securely store that personal information.
Of course students need to be careful when choosing what files to upload, but mistakes happen, and I think design should reflect that.