Why did the Mormon Priesthood ban take so long?

Mormon leaders are reluctant to change policies made by previous prophets as their beliefs lead them to follow the doctrine and policies instituted prior. Many church leaders have stated that they wrestled with the issue of blacks and the priesthood hoping for a clear witness to change the policy. It is unclear why these prophets prior to Spencer W. Kimball did not get the clear revelation they were seeking. Mormons believe that part of progression is to wrestle with difficult issues and exercise agency when not getting clear answers from God. Even with positive confirmation, members of the quorum of the 12 apostles only change policies such as this when united unanimously as a quorum, meaning everyone has received similar inspiration or revelation from God. It therefore stands to reason that even with some or most members of the leadership council including the prophet wanting to change the policy, even one dissenting vote could delay changes for years. It would seem that unanimity did not happen until 1978 under Spencer W. Kimball’s leadership and only after his reported revelation on the subject.  

Many Mormons believe that the revelation comes to the person who was prepared to receive it. In a 1963 letter (to Edward Kimball) written fifteen years before he received the revelation regarding the lifting of the priesthood ban, Spencer W. Kimball wrote, “Revelations will probably never come unless they are desired. I think few people receive revelations while lounging on the couch or while playing cards or while relaxing. I believe most revelations would come when a man is on his tip toes, reaching as high as he can for something which he knows he needs, and then there bursts upon him the answer to his problems.”