I suspect Nunno knew the Millers would never leave, no matter what he did. They lived super close to the gym, they attributed Shannon's success to him, Shannon had only been an elite with him. And its clear that the Millers felt 1995 was a hugely important year to making Atlanta, they would never consider uprooting Shannon to go to another gym.
Nunno knew he could scream and yell and have temper tantrums all he wanted, Shannon Miller wasn't going anywhere. And the Millers knew Steve could threaten to kick them and Shannon out all he wanted, but she was the golden goose, he'd always relent and let her back in the gym. Neither party had any incentive to change.