And so to the question.
Why did God err?
You assumed He erred? Did He? I think not.
I think He created Man with the capacity to freely love in obedience, but that came with the built in choice to err on the side of selfishness.
No, God knew /knows exactly what He is doing when he relinquishes power to the mere creation that is human.
A great risk? Yes, some will pursue the short term glory of the here and now, wealth, power, status, hedonism, and trade this in to forget about God.
Others will forego the earthly pleasures, and remembering their Creator, believe in Him and His promises, and love Him.
And oh what love this is.
This is the tenuous love so fragile, so threatened, but so pure, dependent not on comfort and joy today, but on the truth of the promise that although this present life may be tough even to the point of suffering and death, this love surpasses the grave, and the eternal life promised can be tasted right now, in this life, through the power of the Holy Spirit, the mysterious but real counsellor and comforter, who does not alleviate our suffering, but stands with us through all travails, whether physical or mental hardship, financial or material problems, family or relationship traumas, and let's us know we are not suffering alone.