system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] Why did Darth Vader give up on overthrowing the Emperor and ruling the galaxy as Father and Son?

In Episode 5 he makes it clear that this has been his goal for a while, the current expanded universe also shows that pre-episode 5 he learns the identity of the rebel pilot, and starts to put his plans in motion.

However many months of planing leads up to Darth Vader offering Luke a chance to "Rule the galaxy as Father and Son".

The next time we see Vader, he is sub-servant to the Emperor once more, "You don't know the power of the dark side. I must obey my master." and later "It is too late for me, son. The Emperor will show you the true nature of the Force. He is your master now."

I get that Vader didn't wish to leave the Dark Side (until the very end), and Luke didn't wish to leave the Light Side. But Vader abandons all ideas of overthrowing the Emperor, just accepting that he will be treated as a disposable asset if the Emperor does turn Luke.

Why is this?
gpt
Luke wasn't committed to the idea. Vader isn't going to go out on a limb and try to overthrow the Emperor with him right there. Vader isn't powerful enough to take on Palpatine alone. He *needs* Luke to fight with him.