Why did Jesus commit Mary into the care of the beloved disciple, not James, who is known as his brother? According to John's Gospel Jesus on the cross committed his mother to the care of the Beloved Disciple, not to his brother, James. Admittedly James was not there. However, I wonder if this indicates that Mary was Joseph's second wife (as some have said) and that James was the Son of Joseph but not of Mary and Jesus was her only child. I know there are differences among churches about the duration of Mary's virginity, and proposals that Joseph also was a lifelong virgin, but I am looking for opinions that do not rely on dogma.
Jesus’ Mother and Brothers
46 While Jesus was still talking to the crowd, his mother and brothers stood outside, wanting to speak to him. 47 Someone told him, “Your mother and brothers are standing outside, wanting to speak to you.”
48 He replied to him, “Who is my mother, and who are my brothers?” 49 Pointing to his disciples, he said, “Here are my mother and my brothers. 50 For whoever does the will of my Father in heaven is my brother and sister and mother.”
(Matthew 12:46-50)
Because John the beloved does the will of Jesus' Father in heaven. That is why Jesus made John His brother (as Mary's son).
So, this was the reason why John (the beloved) became Jesus' brother (or Mary's son) and his mother Mary. The crowd knew Jesus' brothers, and so they are his biological brothers including James (Matthew 13:55).