The members of the house of Israel were scattered because of their unbelief.
4 And I command you that ye shall write these sayings after I am gone, that if it so be that my people at Jerusalem, they who have seen me and been with me in my ministry, do not ask the Father in my name, that they may receive a knowledge of you by the Holy Ghost, and also of the other tribes whom they know not of, that these sayings which ye shall write shall be kept and shall be manifested unto the Gentiles, that through the fulness of the Gentiles, the remnant of their seed, who shall be scattered forth upon the face of the earth because of their unbelief, may be brought in, or may be brought to a knowledge of me, their Redeemer.
Elder Bruce R. McConkie wrote:
“Our Israelite forebears were scattered because they rejected the gospel, defiled the priesthood, forsook the church, and departed from the kingdom. They were scattered because they turned from the Lord, worshiped false gods, and walked in all the ways of the heathen nations. They were scattered because they . . . rejected the Lord Jehovah, who is the Lord Jesus, of whom all their prophets testified. Israel was scattered for apostasy.”
(A New Witness for the Articles of Faith , 515.)