I am currently reading Countdown to Zero Day which, amongst other things, describes Stuxnet in lay terms. It states that Stuxnet could report to two command and control servers.
Most basic definitions say command and control servers allow a hacker to communicate with or through the malware that's phoned home and as such they can do mischief on the infected machine.
If the Natanz facility was the only target of interest and if it was air gapped then you can't do any of this. Furthermore, Stuxnet was self sufficient in its objective - it didn't need any further interaction once it had found a suitable target.
Other than being made aware of when the cat is out of the bag, why would a hacker need command and control servers for malware that primarily shouldn't have ever made it on to the internet?