Originally posted by: goofyCat
I googled it out of curiosity 😃And found this.
This is for a different song from the same movie, but the reason might be just the same.
Ajab hai dastan teri ae zindagi, Mohammed Rafi —Shararat (1959):
The music here was by Shankar Jaikishan (S-J), who rarely used Kishore. Trivia has it that Kishore Kumar was not the original choice for lead and that some songs had already been recorded when he joined the cast of this movie that also included Meena Kumari. Though Kishore had already sung numbers like 'Dukhi man mere' for sad occasions, the second antara of this song makes you feel that it needed Rafi’s high-pitch while reaching the crescendo during 'tumhare pyaar ke.' The piano prelude is vintage S-J and reminds you of 'Dil Ke Jharoke Mein' and 'Bahaaron Phool Barsao.'