It could be that he's too focused on the task or situation at hand to respond immediately. In addition, he may think that communicating with you is not a high priority among what he is doing. You can try to remind him that you want to communicate with him before he starts doing anything, or try to interact with him in other ways, such as sending a simple greeting or message, to see if it will help. In addition, communication should be mutual. You should also try to understand what he is paying attention to and what he wants to communicate with you. This can help you better understand his thoughts and needs and find a better way to communicate.