I had the job in the US, my wife didn't. Even if she did have her own E-3 visa that could have been jeopardized by my including her on my green card application on my H1B visa.

EDIT: The principal at the school where my wife was volunteering actually wanted to hire her as she was better qualified than some of the paid instructors she was helping. But at some level higher up the chain they had a policy of not sponsoring work visas, so that went nowhere.