This question already has an answer here:
I saw this question on Stack Overflow: How does this user earn the Popular and Notable question badges without a corresponding question?, and it made me wonder why badges are not "unawarded" like reputation when questions or answers are are changed or deleted.
Why are badges not unawarded when a question or answer's disposition changes?
There's a related un-answered/un-discussed question at Remove badges for deleted or migrated posts. In the previous question, the authors makes a feature request to unaward them. This question asks why things are the way the are.