In "Star Wars: Episode III - Revenge of the Sith," Tarps (the character portrayed as a Sith apprentice) does not exist within the official canon of the Star Wars universe. It appears you may be referring to a fan-created content or a different character altogether.
However, Anakin Skywalker’s transformation into Darth Vader is primarily influenced by Emperor Palpatine, who expertly manipulates Anakin by exploiting his fears, desires, and insecurities. Anakin's emotional turmoil, including his attachments to Padmé Amidala and his fear of loss, plays a significant role in his fall to the dark side.
If you're asking about why a specific character or entity failed to manipulate Anakin in a particular storyline or fan fiction, it would depend greatly on the specific interactions, motives, and narrative choices presented in that story. Often, characters that seek to manipulate Anakin may fail due to his strong will, complex emotions, or a realization of their true intentions.
If you have a more specific context in mind or a particular storyline involving Tarps, feel free to clarify!