Why did he stand there and let Kilo Ren kill him?
Kylo Ren didn’t kill him, the force projection was incredibly draining and he was going to die anyway.
That is not clearly explained in movie, and why was he “going to die anyway”?
Not explained, but recall how he looked and acted when he “awoke” on Ach-To. The projection took an immense amount of energy, enough to kill him. When I say he was “going to die anyway,” I mean that whether or not Kylo swung at him, he was going to die when he awoke.
sorry not buying it.
and why didn’t he try to kill Kilo Ren right there?
He couldn’t. IIRC he wasn’t able to physically interact with the world, at least not to that extent, he was just a projection.
This is not clearly explained in the movie either.
It wasn’t explained because it didn’t need to be, Rian did a very good job at showing and not telling. It was shown when Luke dragged his foot across the salt without making a mark.
Not good enough, I was confused by the whole thing and I sure I’m not the only one.