Why did Stuxnet affected non nuclear industrial control system.

I understand that Stuxnet is capable of spreading to non nuclear industrial control system,but after infecting a non nuclear control system why did it negatively impacted those control systems. It would have been like "I have code to hinder a nuclear centrifuge, but this machine seems to be control system of non nuclear factory and I have no clue what to do other than end of code reached".

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