The idea is, that the subject of the photo "pops" (in the words of Apple).
Edit: and I think, a part is just "because we can", now that photos have the required depth information.
It’s a trick that graphic designers have been doing to magazine covers and such for ages now. But now we have the tech to pull the subject out automatically.
It works even with non-portrait photos that don't have depth information
It looks good and I agree.
What’s the idea behind doing this?