The space on Nephi's plates are limited and difficult to write. Enos who had to confron this space limitation wrote in a condensed form, the plan of salvation, receiving the second comforter and having his calling and election made sure. Nephi commanded his posterity that they do not occupy the plates with that which is of no worth. The book was written for our day, to come forth by the gift and power of God. As Nephi knew, we would have Isaiah's words. Why would he waste precious space repeating what we already had? Nephi was forbidden from revealing what the Lord had shown him in the end of his vision, yet, if other prophets had prophesied the same things, and if he could make minor revisions to these would he not want to warn us of the problems we, who would recieve the book, would face?
"Hearken and hear this, O house of Jacob, who are called by the name of Israel, and are come forth out of the waters of Judah, or out of the waters of baptism1, who swear by the name of the Lord, and make mention of the God of Israel, yet they swear not in truth nor in righteousness." (1 Nephi 20:1)
"Nevertheless, they call themselves of the holy city, but they do not stay themselves upon the God of Israel, who is the Lord of Hosts; yea, the Lord of Hosts is his name." (ibid. v. 2)
"And I did it because I knew that thou art obstinate, and thy neck is an iron sinew, and thy brow brass" (ibid v. 4)
"O house of Jacob, come ye and let us walk in the light of the Lord; yea, come, for ye have all gone astray, every one to his wicked ways." (2 Nephi 12:5)
"Their land also is full of silver and gold, neither is there any end of their treasures; their land is also full of horses, neither is there any end of their chariots. Their land is also full of idols; they worship the work of their own hands, that which their own fingers have made. And the mean man boweth not down, and the great man humbleth himself not, therefore, forgive him not." (ibid v. 7-9)
"And my people, children are their oppressors, and women rule over them. O my people, they who lead thee cause thee to err and destroy the way of thy paths." (2 Nephi 13:12)
1. Nephi's clarification is not in Isaiah.