Because it's a myth. Photographic memory isn't real. Check out the wikipage on eidetic memory. People that claimed it in the past were not telling the full truth. There are only a few examples of savants being able to recall specific things after one showing, but it's terribly narrow. Like being able to draw a horse you saw, but not human faces.

https://en.wikipedia.org/wiki/Eidetic_memory

there are a lot of book teach you writing note later and give client deep impression.