Conversation so far:
Who was cast as the lead actors of Om Shanti Om?
Shah Rukh was cast as the lead. Padukone was cast as the female lead without a screen test.
Who was cast as the lead actress of Om Shanti Om?
Padukone was cast as the female lead without a screen test.
Who made the casting decisions of Om Shanti Om?
Farah Khan was in charge of casting.
Were there any difficult casting decisions for Om Shanti Om?
Rampal was approached by Khan and Shah Rukh for the part of Mukesh Mehra. Rampal was reluctant to do the role as he felt it was too evil.
Were there any issues with the actors of Om Shanti Om?
Dev Anand refused be in the musical number as he always played lead roles in his career. Amitabh Bachchan refused due to his son's wedding.

Question: Why did they refuse to do those scenes?
Self-contained rewrite: Why did the multiple actors and actresses refuse to do the musical number scenes?