Because unbelievers have no faith, and even many of those who believe have little, "God can do no miracle among them." (Moroni, Ether 12:12) "Yea, and even all they who wrought miracles wrought them by faith, even those who were before Christ and also those who were after." (Ibid., 16)
It is the case with many of us, we go our way, day-by-day, forgetting His wisdom and guidance. The task and trials of life absorbs us, and crowd all thoughts of God from our hearts. In that condition of mind, we reject even His great Name; we "know not the God in whom" we "should trust." To eyes that are blind and hearts that are hardened to the word of the Lord, that He can do no miracle among them, again may we offer one of King David's Psalms, also a Jewish rendition; it awakens in nearly every one a sense of remorse when they think of these last words of Moroni, "They know not the God in Whom they should trust. Answer me when I call, O God of my righteousness, Thou Who didst set me free when I was in distress; be gracious unto me, and hear my prayer. O ye sons of men, how long shall My glory be put to shame, in that ye love vanity and seek after falsehood? But know that the Lord hath set apart the godly man as His own; the Lord will hear when I call unto Him. Tremble, and sin not; commune with your own heart upon your bed, and be still. Offer the sacrifices of righteousness, and put your trust in the Lord. Many are they who say: O that we could see some good! Lord, lift Thou up the light of Thy countenance upon us. Thou hast put gladness in my heart, more than their corn and their wine increase. In peace will I both lay me down and sleep; for Thou, Lord, makest me dwell alone in safety." (Psalm 4)