Because they lost 8 out of 19 aircraft. An unacceptable loss rate at the time and something which appalled Barnes Wallace. 53 (out of 133) aircrew who participated in the attack were killed, near enough 40%. That's almost a suicide mission in western military terms.
Would you care to evidence the "substantial" effects on German production? The longest lasting effect, and hardly critical, was on food production.
None of that diminishes the ingenuity of the raid nor the bravery of the men who carried it out. It was a remarkable achievement.
Cheers
Steve