Because they turned back from him (On the sin of "turning back," see 2 Kings 17:15, 2 Kings 17:16; Proverbs 26:11; 2 Peter 2:22.) And would not consider any of his ways (comp. Psalms 28:5; Isaiah 5:12).
The folly and wickedness of such conduct is reproved by Solomon in the strongest terms, "Because I have called, and ye refused: I have stretched out my hand, and no man regarded; but ye have set at nought all my counsel, and would none of my reproof: I also will laugh at your calamity; I will mock when your fear cometh; when your fear cometh as desolation, and your destruction cometh as a whirlwind; when distress and anguish cometh upon you.
Thou shall they call upon me, but I will not answer; they shall seek me early, but they shall not find me: for that they hated knowledge, and did not choose the fear of the Lord: they would none of my counsel: they despised all my reproof.
Therefore shall they eat the fruit of their own way, and be filled with their Own devices. For the turning away of the simple shall slay them, and the prosperity of fools shall destroy them" (Proverbs 1:24-32).