I understand your view.Because of travel restrictions, many PR holders waiting to land in CANADA (before 18 March 2020 or later issued COPR). They knew that if they issue new COPRs to Outlanders, will be expired in some cases and they have to do re-work on that cases and eventually they stuck in old files rather than new ones. For that they have to bind to Inland files and Student-Family Application from outland. It's simple.
But if students can enter to Canada why can't PR applicants ?
If they don't want to allow PR holder that's fine but at least they can complete other process, eg. MR..