Why did sundiata not walk after receiving his mothers treatments but did not walk when his half brother was made king?

Sundiata's condition did not respond to his mother's sorcery, and he was not able to walk when his brother was made King. It wasn't until after he heard his mother humiliated and felt her pain that he called the blacksmith and received the rod that would strengthen his resolve and allow him to aride and become what he was meant to be. Sundiata's greatest strength was found in compassion.