As you say that we are respecting because he is alive. Are other masoomen not alive according to islam because we are regularly sending salam to every masoomen and salam is for those people who are living? Other thing that we are giving such respect because he is our times imam, then why this things cant be found in the past except 12th Imam. I dont remember such activity for other masoomen at their time. So my humble request to explain it please. I am not satisfied from your answer so please explain .

Yes it’s true that other Aimmah who are not physically prevalent amongst us but have this authority from Allah (swt) to help anyone who asks help from them but their presence and the presence of 12th Imam is different. Our Imam of time is our Living Imam and we have much more responsibilities for him one of them to give him respect as if he is in front of us.