Explanation
It performs better than the same creative run from a brand account for a straightforward reason: the post reads as a person's content with spend behind it rather than as an advertisement, on surfaces where being read as an advertisement is expensive.
It requires a specific, separate permission and usually a separate fee, because the creator is lending their identity rather than delivering a file. That distinction is why it sits in a different part of a contract from ordinary usage rights.
The common mistake
Assuming a usage licence covers it. Permission to use a video is not permission to run it under someone else's name, and the two are priced and negotiated separately.