I'm guessing it's part of the game, so that you Sims can pick up a career where they left it in case they want to go back? Not sure.
The cheat for it is:
1. Open console, and do "testingcheats true", without quotes;
2. Quit current job using the phone;
3. Open console, and do "Careers.add_career <NameOfCareer>", without quotes or brackets, and the career's name instead of "NameOfCareer".
Source here.
Thank you!!!! What I ended up doing was evicting my Sim that I wanted the writer career and editing him a little in CAS and then moving him back into his house. The problem with doing that instead of using cheats is 1. Loss of money 2. Loss of royalties
he was getting 6 grand in royalties a day!!!!
3. Loss of relationships, yup, they all disappeared
So this kind of sucked. I feel like I am starting from scratch now. He has all of his skills and traits thankfully, but yeah, still sucks that I worked hard to get all that money and those royalties and poof, gone! Relationships take a lot more work to maintain in this game too. So yeah. Oh well lol