That’s because Anakin “died” when he turned to the dark side.
Also, Shaw does look completely different without the Vader makeup. From a saga POV, I can see why George went with Hayden.
I don’t agree with this at all. For one, he doesn’t look completely different, it’s quite clear it’s the same person. Second, anyone with a brain could tell from the context who the new ghost was. And third, it was the old man who saved Luke, not the smirking child killer. And of course, there are the inconsistencies on top of it all.
The only reason George put Hayden in there was because he wanted to sell the prequels as legitimate films. People rejected them as inferior to the OT, he took offense to it, and he hijacked the original movies as a big FU, you must like my prequel films, to the rest of us.