The front camera being a selfie camera, I suppose there is also to some extent the intention to make pictures look similar to what the user is used to see in his/her mirror. I am not saying this is the reason, but I assume it might be one.

It may seem insignificant, but people's symmetry is imperfect, and there really is a huge difference in the impression (and therefore the satisfaction) a mirror image can give, compared to a normal image. It's easy to try with selfies of yourself, comparing them flipped or not, sometimes the "normal" picture is really uncomfortable compared to the mirror image and the user would often prefer the face and haircut he is used to, even if no one else seems them in real life.