You're forgetting that this is a film though. It doesn't make much sense that Anakin take his younger form, while the other two don't. All that does is ake the audience wonder why. Not exactly what they should be focusing on. Just the very act has people believing that Anakin died when he joined Palpatine and that his spirit couldn't cross over as his body was still alive in the form of Darth Vader. It's gone from a metaphorical thing to a literal one, which is ridiculous.