When a reference goes missing, there is no indication in the sketch reference window that there is an issue. All we see is the name of the geometry backup instead of the actual reference name. Most people won't easily use that as an indicator that there is a problem.
On the other hand, the EDIT REFERENCES menu does show the missing references, and uses their real names.
Firstly, the sketch references and the edit references should be consistent in how they portray the references.
Secondly, we would prefer the sketch references look like the edit references. If someone had dozens of references in the sketch and some of them went missing, it would be hard to easily see which ones they were and how to fix them.