The reason behind Lucifer's unusually compliant behavior lay in the aftermath of his manipulation of memories and thoughts with his subconscious. This action triggered a significant backlash, leaving his soul in a weakened state, rendering him unable to process information as effectively as before. Consequently, he found himself more amenable to cooperating with the Twilight Emperor and accepting the mission without resistance. His primary motive was to avoid attracting further scrutiny and prying eyes onto himself, especially in his vulnerable state.