What are your plans for surviving as an apprentice of the Emperor, then?
Palpatine murdered his master, and has always been paranoid that he might be murdered by one of his apprentices. Hence why he's constantly trying to engineer the downfall of his apprentices. He tricked Dooku into being killed by the apprentice Palaptine actually wanted. And then when Luke came along, who had greater potential than Vader, Palpatine then immediately tried to goad Luke into killing off Vader. And even if Luke didn't do it, Palpatine wanted them to kill each other, so whoever lived would be demoralized and more malleable. And if you include Clone Wars, then Palpatine didn't like the idea one of his former apprentices, Darth Maul, still being alive, and tried to kill him off to clean up loose ends.
If you pledge yourself to Palpatine, you're placing yourself in a huge amount of danger. Palpatine will always be reevaluating your potential for power and how easily you will be controlled compared to any other force user, like Vader and Luke. If you're not as powerful as them, or deemed to not be as controllable, then Palpatine might try to dispose of you. If you are a better candidate than Vader or Luke, then they might try to engineer your death so they can climb up the ladder to become more pleasing in the Emperor's eyes. Trying to goad Vader into overthrowing the Emperor is a bad option, because 1. Vader is loyal to the Emperor and might use that suggestion as an excuse to kill you off, and 2. Vader habitually kills his own subordinates so you're playing with fire here.
Oh, and the rest of the galaxy will be trying to kill you.
I don't know. Joining Palpatine is like trying to join Stalin's regime. You're dealing with a paranoid master who is killing off anyone he deems too smart or inconvenient, and you're competing with other officers who are constantly undermining and backstabbing each other trying to gain more favor in the boss' eyes. And the rest of the world is trying to kill you too. Life expectancy = very short.