When Jedis die they can reappear as visions to the people they knew. Why is that a concept that needs further analysis?
Because when Jedi’s die they don’t usually show up as ghosts otherwise there would be nothing special about it. It was Qui-gon first. Then Obi-wan and then Yoda. and then Anakin.
No other Jedi was able to achieve becoming a force ghost. But it had to do with the special teachings of Qui-gon which he had learned and passed on his knowledge. Otherwise there would be millions of Force ghost Jedi floating about.
It has nothing to do with being a Jedi.
Meh. That’s all PT garbage and doesn’t effect the films I watch. And appearing to certain people doesn’t equal “millions of Force ghost Jedi floating about”. If everybody could see 'em, Leia would have said “Hey, Luke! Come join us for a group pic- WHAT THE HELL?? G-G-G-GHOSTS!” But, she couldn’t see 'em. Only Luke.