I've asked this question
out of curiosity and some confused it as a duplicate of
Which was not because I was looking for the reason behind of it.
This is actually a duplicate of Why are some files unmovable when shrinking a partition in Windows? Sadly, the only "answer" at the older question fails to answer it at all. This is not a new issue, nor is it specific to Windows 10. Given the superior quality of the answers here, I'd almost be tempted to suggest removing the "windows-10" tag from this question and making it the canonical version (marking the older question as a dupe to this one).
I asked specifically for Windows 10 since I didn't want to be broad. The question went to HNQ and the answer was very good.
We can remove the windows 10 from the title (maybe with some better words from a native speaker), the answers already did not mention 10, and make this question as a canonical. Should we?