The Sith aren’t exactly known for their honor and loyalty. If a master wanted to replace an apprentice they would find a new one and begin training them first. When an apprentice wanted to replace their master secretly taking an apprentice could help them consolidate power.
https://starwars.fandom.com/wiki/Order_of_the_Sith_Lords#Secret_apprentices
The Sith aren’t exactly known for their honor and loyalty. If a master wanted to replace an apprentice they would find a new one and begin training them first. When an apprentice wanted to replace their master secretly taking an apprentice could help them consolidate power.
I see. Thanks for the illumination