@Pat271
Well, if they would leave some kind of explanation in the private feedback, that would be helpful indeed. However, in the example I gave above, there was none.
The guest herself was very clean and tidy, so perhaps my standards weren't up to scratch for her. However, after I did an interim clean of her room, she commented on how lovely and clean it was. So, there was something else going on there. Why would she rate 5* in everything other than cleanliness?
I also have very rarely asked guests this question, but a couple of times that I did, it turned out to be worthwhile. One was early on when I asked why the guest left 5* in all categories but 4* overall. She was mortified and said she was sure she left 5* overall and there was nothing wrong at all. Airbnb agreed to change the rating to 5* (although not sure they would do that these days) when she confirmed that was the rating she had meant to leave.
The other time was when I asked a guest who seemed happy with her stay and left a completely positive review and private feedback why she left me 3*. She admitted she had no idea 3* was bad and the reason for the rating was because the listing was over her 'initial budget' (she had asked me more than once for an additional discount before booking and then her aunt, a Superhost, seemed to have convinced her to book my place anyway). She told Airbnb to remove the review/ratings, which they did.
So, actually, on the rare occasions I have asked, sometimes it has worked out well. The only other time I asked, it didn't... but it didn't make matters any worse either.