Anakin Skywalker was driven to the dark side of the Force to save Padmé. As we saw in Revenge of the Sith, he was lured to the dark side by Palpatine’s promise to help her “cheat death.”
When she died, it seemed that Anakin would not have a reason to stay with the Emperor.
Since Anakin didn’t get what he wanted, why did he remain a Sith? Much of the explanation concerns the dark side and his lack of options.
Anakin’s Turn to the Dark Side
Anakin’s turn to the dark side transpired from Attack of the Clones to Revenge of the Sith.
On-screen, key intervals included his slaughter of the Tusken Raiders, his pledge of loyalty to Palpatine, and choosing him over Mace Windu.
Between these events, Anakin also killed Count Dooku, shifting him toward the dark side.
As this article conveys, Anakin had numerous moments that added over time to push him to the dark side.
Such moments include when he lost Qui-Gon Jinn as a mentor and father figure, the Jedi did not allow him to check on his mother, his jealousy over Rush Clovis, and Ahsoka’s removal from the Jedi Order (the latter two events depicted in The Clone Wars series).
These more subtle moments collectively corrupted Anakin. More noticeable developments like his marriage to Padmé and her pregnancy likewise set up his downfall.
Anakin took the final plunge because he wanted to save her.
When Padmé died anyway, Anakin could have abandoned the Sith but did not do so.
Why Did Anakin Remain a Sith?
One fan post lists convincing reasons for why Anakin remained a Sith, including the “significant time and effort” becoming one, his “corrupted values,” and his fear of losing power and the wrath of Darth Sidious.
Among these reasons, “the corrupting influence of the dark side” seems to weigh most heavily, with other posts supporting this point.
Anakin gradually became more enveloped by the dark side like a black hole swallowing him whole. The corruption of the dark side impacts the body and the mind, in Anakin’s case, especially the latter.
His mind became so bent that he believed Obi-Wan and Padmé were plotting against him. Here in their last embrace, we saw Anakin spellbound by his powers and turn on Padmé, Force-choking her until she fell unconscious.
Relatedly, Vader came to embrace power and did not want to give it up. This motive is based on dark side corruption and intertwines with the above reason.
Fueled by the hate of the dark side, Vader became attached to power itself.
As he famously said to Luke in Return of the Jedi, “You don’t know the power of the dark side,” which we can interpret as both its gravitational pull and Vader’s lust for it.
The consequences of defying Sidious were severe. In the comics, we saw the results of challenging Sidious.
After The Empire Strikes Back, Vader looked for answers about Padmé’s death and how Luke could have survived.
That quest brought him to question his loyalty to Palpatine. As this video conveys, Vader then faced “the full power of his Master’s wrath,” complete with devastating Sith lightning.
Other commentary on this topic indicates how Anakin had already “broken his most sacred ethical oaths” with such actions as decimating the Jedi Temple, including Younglings.
He also had “too much self-hate to turn back.”
In Vader’s self-loathing, Anakin became lost and blamed the Jedi for his misfortunes. He could only identify with the Sith.
George Lucas extends this rationale by commenting, before all the extensions of Star Wars, that Sidious is the one who gave Vader/Anakin a special place with the Empire.
Vader did not have many options after everything that had occurred with Order 66 and the loss of Padmé.
Sidious was the one person who would support and cultivate Vader’s “revenge life” and encourage him to “take it out on everybody.”
Being Sidious’s “right-hand guy” was better than being an outcast former Jedi and Sith.
Vader Remained a Sith
Lucas’s explanation brings us to the realization that Anakin remained a Sith because he lacked other options and found support in Sidious. Anakin also became consumed with the dark side and could not see beyond it, until Luke helped resurrect that part of himself.