Sorry it caused you pain. We always have “reasons”. I’ll share this one.
It was a mistake made by an integration engineer moving code from one branch to another and it was the path of least resistance “temporarily” to keep multiple projects working that didn’t have all the code for FUniqueNetId and so were failing to compile “can’t instantiate abstract class”. So it was set non virtual and forgotten about.
Apologies. It was never an intentional design decision. Lots going on around here 