Let's just assume that it's not meant literally that they never uttered a single word to each other for the 8 to 10 years Michael was still living under Sarek and Amanda's roof. "Pass the salt", sure. Answering "Where is mother?", only polite. "Dinner is ready", just passing on information. But sitting in a room together and practicing the Vulcan salute? Talking about the future and making plans to one day live on earth together? That stops. Instead of seeking each other out, avoidance. Michael is in the living room area? Spock will be in his room. At the table Michael talks to her parents, Spock talks to his parents, but they don't talk to each other. And given how long Spock and Sarek were able to hold a grudge against each other, Spock might easily have maintained ignoring any overtures by Michael until she finally got the hint and stopped. That is, if there were overtures, and she hadn't convinced herself at the time that pushing Spock away was only "for the best".