The Big Bang Theory ended after 12 seasons not because it was canceled, but because Jim Parsons, who played Sheldon Cooper, decided not to renew his contract for season 13. 

Despite the show's success, Parsons wanted to move on with his acting career and life. The rest of the cast had mixed feelings about the ending, with Kaley Cuoco being "in shock" and Mayim Bialik acknowledging that there were undisclosed factors behind the decision.

 Young Sheldon, a spin-off prequel, has been successful and recently renewed for a seventh season, while another spin-off sequel is currently in development. Overall, the former cast members have continued to pursue their careers in various projects since the show's conclusion.