Not only is it a cheap fan service moment that would feel fan Edit-y, it doesn’t make any narrative sense to have Anakin there. The whole point of the scene is to show Rey adopting the skywalker name after the people who have impacted her the most: Luke and leia, adding Ben makes the most sense because the whole trilogy is about his redemption. Yes, Rey has heard Anakin’s voice during the climax but she does not know what he looks like. If Anakin appeared there it would not make sense for Rey to see him as Anakin pretty much doesn’t mean much to her. In the same sense it would also be weird if in return of the Jedi luke saw Qui-gon for the same reasons. The force ghosts are meant to appear to people who they have left impacts on. Luke would only see Anakin, obi wan and yoda because they left impact on him. Obi wan in clone wars talks to Qui-gon because that’s his former master, and rey would see luke and leia (and should have seen ben) for the same reasons.