M'rk, son of Mogh wrote:
How many more times do I have to repeat myself?
Shinzon's motivations are all about Reman nationalism: He wants to liberate the Remans and is against the Romulans.
Keep repeating yourself, it doesn't change what we all see in the movie.
You are correct. Shinzon's motivations were about liberating the Remans and opposing the Romulans. That part of the story still occured, it was the opening scene.
He succeeded. He won.
Don't be ridiculous. He overthrew the Preator, but that just meant that someone else might overthrow him
. Installing himself as Praetor made him dependent on the Imperial Fleet for their support, and that meant that the liberation of the Remans was still a work in progress at best. Saying that his taking the Praetorship meant that he'd "won" is as ridiculous as saying that African Americans aren't still oppressed just because the President is black.
That's why it makes no sense that he'd suddenly fixate on Earth: There's no indication earlier in the film that he gives a damn about Earth, and no reason for him to care about Earth when the liberation of the Remans wasn't done yet.