Occasionally a student will leave the school and return later. When they re-apply, the parent may create an entirely new record. When this happens, it might be well into the new year before the duplication is found - and then it's a big problem.
When merging records, "things like entering years can be moved, but course enrollments can not." -Blackbaud Support.
Given non-overlapping enrollments, it should be possible to merge student records.
This is also confusing for the parents, as they see the same student twice when looking at academic and financial information, and it is not clear (from the student name) which is the current record.
It also looks terribly unprofessional.