Because you took it with a mobile phone and most likely an Apple one.
What you have to do is save the photo to your computer, then rotate it with your favourite picture editing application then "save as" or "save a copy" using a different file name .
I will then appear correct on the forum.
You are correct that I took the pic with an Apple cell 6S. I DID save it to my pc, rotated it, saved, and it still comes out 90 degrees rotated. I did not save it as a different file name. Thanks for the info. Maybe one day I will get out of the 3rd grade in my pc education.