John Watson does not speak. It's a fact of life, an answer. No one questions it because they know. They know he stopped talking when Sherlock was pronounced dead, when John had to go in to identify the body. Three years, the doctor went without speaking a word, not even a whisper. He lost friends, lost hope. Nobody could stand the sad, withdrawn look in his eyes when they asked "Why don't you speak?"
John H. Watson was trained to survive, to cope in any way he could. How to live in extreme situations. Losing Sherlock was an extreme situation, because you can't make someone better and leave. You can't put a bandage on the wound only to rip it off and yell "Just kidding!"
Three years straight of silence, and no one could imagine the things he yelled when he found out Sherlock was alive.